MXPA98002085A - Preamble of modality of rafa - Google Patents

Abstract

In a burst mode communication system (Figures 1 and 2) bursts of information with a known preamble (402) Figure 4, are transmitted from a burst mode transmitter and are received by a burst mode receiver that uses the preamble to determine the presence of a burst and determine the correct frequency of the carrier, the carrier phase, the frequency of the clock symbol and the phase of the clock symbol in order to correctly recover the transmitted symbols and thus the information contained within the gust. The present invention involves a burst transmission method using preamble (402) containing an initial pulse (420) and a Barker sequence (440) following the initial pulse separated by a dead time period (430) equal to the time of transmission of at least one symbol. The preamble can be transmitted on orthogonal carriers (Fig. 5) and the order to the Barker sequence (440) can be inverse and multiplied by minus one on one of the carriers to reduce the probability that noise events on both carriers will the least detectable Barker sequence on each can

Description

PREAMBLE OF MODALITY OF R FAGAS Cross-references This application claims the benefit of the U.S. Provisional Application. No. 60 / 005,444 filed on October 12, 1995, entitled "Preamble for the Reception of Burst Modes" whose inventor is Lawrence Ebringer, with the lawyer's file No. NP2008.

Background of the Invention Burst mode transmitters generally need to transmit a training sequence or a preamble prior to data transmission, so that a burst mode receiver can obtain the phase of the correct clock sample and the phase of the protractor to recover the information or data.

Compendium of the Invention In a burst mode communication system that has a burst mode transmitter using a Quadrature Phase Change Transmit modulation, the burst containing a preamble and information is transmitted first by transmitting a pulse of one to three symbols of long, waiting for a timeout to three long symbols during which time symbols are not transmitted; transmitting a Barker sequence of at least seven bits long in both I and Q channels and transmitting the information.

To reduce the effect of noise in the Barker sequence, the sequence can be reversed and inverted in the I and Q channels, such that channel I contains a sequence and channel Q contains the same Barker sequence in inverted order and multiplied by minus 1.

An advantage of the present invention is that many different types of burst mode receivers can be used to detect the burst and recover the transmitted information based on a short preamble.

Brief Description of the Drawings Figure 1 represents a communication medium shared with multiple burst mode transmitters and a single burst mode receiver.

Figure 2 illustrates a Fiber network for Restriction (FTTC) with a subscriber's coaxial cable network forming a shared communication medium. In the illustrated FTTC network, a Host Digital Terminal 230 (KDT) is connected to the Public Switched Telecommunications Network (PSTN) 210 as well as a Transfer Modality network Asynchronous 220 (ATM) and one or more Optical Network Units (ONUs) 240 through fiber optic 260. The Unit of Broadband Interface (BIU) 250 at UN 240 contains, transmits and receives circuits to send signals to devices in a residence 290.

The devices in the residence 290 are connected to the BIU 250 through a coaxial cable network of the subscriber, which when used in the present, is defined as a network comprising a coaxial cable 270, a separator 280, and an internal coaxial wiring 272 that connects an individual residence 290 to the BIU 250. The use of the term subscriber indicates that the client in the residence is a potential subscriber or subscriber for the services provided by the telecommunications network FTTC. The network of the coaxial cable of the subscriber forms a means of shared communication, since it allows all devices connected to it, access to the BIU 250 with non-active switching.

As shown in Figure 3, examples of the types of devices that may be presented at residence 290 include a telephone connected to a Prize Interface Device (PID) 29β, a computer containing a Network Interface Card 292. and a television 299 with a "settop" 298. The computer contains a letter NIC 292. The PID 296 and the "settop" 298 can transmit the signals to the 3IU 250 through the internal coaxial wiring 272, the separator 280 and the cable tensioner 270.

II Communications of the Burst Modal in a system In the FTTC system digital signals are used to carry a voice, video and data signals to the devices.

The protocols and formats of the Transfer Modality Asynchronous (ATM) can be used to carry signals.

The system requires bidirectional communications between the devices of the residence 290 and the ONU 240, and the information is transmitted in the return direction, for example, from the devices to the ONU 240 to change the channels in the television 299, sustain a voice conversation over the telephone 294, or using the network services in the computer with the letter NIC 292. The system provides cells for the transport of ATM in the return address, as well as in the forward direction (ONU to devices ).

The shared communication medium formed by the subscriber's coaxial network suggests that the devices use a multiple access protocol to transmit to the BIU 250 at ONU 240. A number of multiple access protocols can be used, including Multiple Access.

Division of Frequency (FDMA), Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) When the TDMA protocol is used, the devices will have opportunity opportunities for transmissions to the BIU 250, and when the ATM protocols are used, one or more cells will be transmitted in the opportunities.

Although the signals can be transmitted in the subscriber's coaxial cable network in the form of a baseband from where the separator 280 has the appropriate low frequency characteristics, it is generally more appropriate to transmit signals both forward and in the return direction over the signals of the free transmission band that are centered around some non-zero frequency.

Figure 3 illustrates a possible spectrum of forward and backward signals in a coaxial network of the subscriber with a forward carrier of the FCTT 310, and a return carrier of the FTTC 320. In a modality of an FTTC system, the transmission forward is carried out in a forward carrier of FTTC 310 at a frequency of 38.88 MHz. with a data rate of 19.44mb / s using the Quadrature Phase Shift Transmission (PSK). An advantage of this mode is that the spectrum of the TV signals above 50 MHz are not disturbed by these transmissions, if a similar signal is present in the coaxial network of the subscriber. However, this mode offers only one example and several frequencies, data proportion and modulation formats can be used to practice the invention. It should be noted that the techniques commonly referred to as Carrierless Amplitude Phase Modulation (CAP) are subsequent to the generation of a signal, equivalent to the QPSK and QAM modulation formats.

III Preamble for communications of the burst mode Figure 4 illustrates the structure of a burst for a burst mode transmission. It can be received using a number of methods and consists of a preamble 492 followed by the data 404. The preamble has a pulse 420, a dead time 430 and a Barker sequence 440.

The Barker sequence is used in a preferred embodiment of the invention because it has a low cross-correlation and high autocorrelation properties. In the preferred embodiment, the transmitter uses the Quadrature Phase Change Transmission modulation, (QPSK) wherein the binary symbols are modulated on the orthogonal carriers referred to co or the I and Q channels. It can be thought of the carriers with different frequencies in the sense that the complex representation of the orthogonal carriers are different even when the actual value of the frequency is the same. The Barker sequence consisting of 1-13 bits can be transmitted in the preamble over both bearers.

Because the noise on the orthogonal carriers can be correlated, there can be a correspondence between the errors in the signals detected in the receiver of the burst mode. To reduce the likelihood that noise events on both carriers make the Barker sequence less detectable on each channel, the order of the Barker sequence can be reversed in one channel with respect to the other channel. To further reduce the event of correlated noise events, the Barker sequence in channels I and Q can be inverted with respect to each other, as well as transmitted in different transmission sequences in channels I and Q. As an example, the Barker sequence can be transmitted from the beginning to the end in the I channel, and in an inverted form from the end to the beginning in the Q channel.

Figure 5 illustrates the preamble sequence of a modality that integrates a binary "1" in both channel I and Q, followed by a dead time of two symbols, during which time no signal is transmitted, followed by by a 13-bit Barker sequence in the I channel and in the same reverse sequence and inverted in the Q channel.

A person skilled in the art will recognize that a Barker sequence can be modified without substantially altering its cross-correlation or autocorrelation properties. It will also recognize that Barker's sequence can understand more than one Barker word code. In a preferred embodiment of the preamble, the initial pulse-and the dead time are followed by a 13-bit word code of Barker that is subsequently followed by a binary sequence that is different for channel I and for channel Q. In one preferred modality the preamble is 1 = 1 0 0 1 1 1 1 1 - 1 1 1 1 - 1 1 - 1 1 1 1 1 1 1 1 1 1 Q - 1 0 0 - 1 1 - i 1 1 - 1 - 1 1 1 - 1 - 1 - 1 - 1 - 1 1 1 1 - 1 1 - 1 - 1 The number of ones on the pulse 420 can vary with a single event of one being the obvious minimum to be able to detect the presence of a pulse in a receiver. More than a single '1' can be transmitted, but it can cause the unnecessary lengthening of the preamble. When transmitting to one on both I and Q channels, it is possible to use a measure of power at the receiver to detect the presence of the pulse. Since carrier recovery is typically not presented when the put arrives, only a measure of power is possible, and the use of one in both I and Q channels allows a measure of non-coherent power to be used. to detect the pulse.

The dead time 430 is provided to prevent precursors' that can be formed in the filtering of the Barker sequence 440 in a burst mode 120 receiver from the interference with the reception and detection of the pulse 420 and vice versa.

The information or data is subsequently transmitted in the form of binary modulated symbols on the orthogonal carriers using QPSK modulations.

In another aspect, the invention comprises a burst mode transmitter for use in a burst mode communication system. The burst mode transmitter is capable of generating bursts for transmission to a burst mode receiver. The burst mode transmitting circuit for producing burst signals in general is known in the art. The bursts of the present invention comprise a preamble and information that is encoded in binary and modulated symbols at a first carrier frequency and at a second carrier frequency wherein the second bearer frequency is orthogonal to the first bearer frequency as before. he described. The preamble consists of a sequence of data pulse followed by a Barker sequence. The data pulse and the Barker sequence are separated by a transmission time period equivalent to the transmission period of at least one, preferably two binary symbols.

The burst mode signal is transmitted through a shared communication medium, and is received by a burst mode receiver that uses the preamble to determine the presence of a burst and determine the correct frequency of the carrier, the bearer phase , the symbol clock frequency t the phase of the symbol clock in order to correctly recover the transmitted symbols and thus the information contained within the burst.

As an example of a method of recovering a burst mode signal is the use of a fractionally spaced transverse coupled equalizer structure which is preceded by an initiator circuit which senses the presence of the pulse 420 and uses the Barker 440 sequence for the adjustment of the equalizer noises for the clock and the recovery of the carrier phase.

The reception of the burst mode signal can be carried out by converting a received analog signal into a digital signal and subverting the digital signal e a baseband signal having an I channel and a Q channel with at least two samples per symbol. The presence of a burst is determined by examining the square values of at least three samples and determining through the use of at least the threshold, if a burst is present, and if so, which of the samples is closest to the center of a predetermined symbol in the preamble.

The signals on the I and Q channels are passed through digital filters with noise that can be adjusted to minimize an error signal that is produced by means of a subsequent decision circuit that performs the thresholding of the filtered samples and makes the determinations of the values of the symbol and correlates the recovered symbols with a stored version of the predetermined preamble during the training mode, or with the previous examples form the thresholds during a normal mode of operation. The correlation produces an error signal that during the training mode represents the initial error while the filters are adjusted to obtain the sampling phase of the appropriate symbol and minimizes the displacement of the carrier phase, and which during the normal mode of operation represents the deviation in the sampling of the symbol and the phases of the carrier. Minimizing this error signal during the training phase results in the recovery of the sampling phase of the symbol and the acquisition of the carrier phase, and during the normal mode of operation resulting in a tracking of the symbol and carrier phases.

The preceding description of a receiving method and architecture for the reception of the burst mode is given as an example only, and alternative architectures for burst mode receivers are possible.

Although the present invention was described in considerable detail with reference to certain preferred versions thereof, other versions are possible. However, the goal of the invention as a method and apparatus for the transmission of the burst mode information remains the same. An application of the invention is the transmission of information transmitted from a burst mode device located in a residence 290, an example of which is a "settop" 298 connected to a television 299, a BIU 250 in a ONU 240 of an FTTC system. In this application a subscriber can carry out a channel change operation or other related video function through the remote control of a "settop". This information is transmitted in the form of a burst from the settop 298 to the BIU 250, to the ONU 240 and to the HDT 230, which can make the change or require another element of the network of the ATM network 220 to effect the change. The ability to transmit the bursts of the settop 298 and be correctly received by a burst mode receiver is essential to correctly interpret the subscriber's commands. Therefore, the spirit and scope of the appended claims should not limit the description of the preferred versions contained herein.

Claims (15)

1. In a burst mode communication system having bursts containing a predetermined preamble and data which is encoded in binary and modulated symbols in a first bearer frequency and a second bearer frequency in which the second bearer frequency is orthogonal to the first carrier frequency; a method for transmitting said burst comprises; a) the transmission of at least one symbol indicating a binary on the first bearer frequency and at least one symbol indicating a binary on a second bearer frequency; b) subsequently wait for a period of at least one symbol, during which time symbols are not transmitted, and; c) Subsequently, transmitting a binary Barker sequence with a length of at least seven bits and having a beginning and an end on the first frequency of the carrier and simultaneously transmitting the binary sequence Barker with a length of at least seven bits and having the beginning and the end on the second frequency of the carrier; d) Subsequently, the transmission of information in the form of binary symbols modulated on the first and second carrier.

2. The method of claim 1, wherein the Barker sequence has a length of at least thirteen bits.

3. The method of claim 1, wherein the Barker sequence is transmitted from the beginning to the end on the first frequency of the carrier and is transmitted simultaneously from the end to the beginning on the second frequency of the carrier.

4. The method of claim 2, wherein the Barker sequence is transmitted from the beginning to the end on the first frequency of the carrier and is transmitted simultaneously from the end to the beginning on the second frequency of the carrier.

5. The method of claim 1, wherein the Barker sequence is transmitted from the beginning to the end on the first frequency of the carrier and is transmitted simultaneously from the end to the beginning and inverted in sign on the second frequency of the carrier.

6. The method of claim 2, wherein the Barker sequence is transmitted from the beginning to the end on the first frequency of the carrier and is transmitted simultaneously from the end to the beginning and inverted in sign on the second frequency of the carrier.

7. A burst mode communication system comprising a burst mode transmitter, a burst mode receiver, and a transmission medium between the burst mode transmitter and a burst mode receiver wherein the burst is transmitted from the burst mode transmitter to the burst mode receiver and the bursts comprise a preamble and information that is encoded in the binary and modulated symbols on a first bearer frequency and a second bearer frequency wherein the second bearer frequency is orthogonal to the first frequency of the carrier, and wherein the preamble comprises a sequence of data pulse followed by a Barker sequence; the data pulse and the Barker sequence are separated by a transmission time period equivalent to the transmission period of at least one binary symbol.

8. The burst mode communication system of claim 7, wherein the Barker sequence has a length of at least thirteen bits.

9. The burst mode communication system of claim 8, wherein the Barker sequence comprises a thirteen-bit word code.

10. A burst mode preamble for use in a burst mode communication system having bursts containing data that is encoded in binary and modulated symbols on a first carrier frequency and a second bearer frequency wherein the second frequency of carrier is orthogonal to the first frequency of the carrier; the preamble of the burst mode comprises a sequence of a data pulse followed by a Barker sequence; this data pulse and the Barker sequence are separated by a transmission time period equivalent to the transmission period of at least one binary symbol.

11. The preamble of the burst mode of claim 10, wherein the Barker sequence has a length of at least thirteen bits.

12. The preamble of the burst mode of claim 11, wherein the Barker sequence comprises a thirteen-bit word code.

13. A burst mode transmitter for use in a burst mode communication system, this burst mode transmitter comprises means for generating burst for transmission to a burst mode receiver; these bursts comprise a preamble and information which are encoded in binary symbols and are modulated in a first carrier frequency and in a second bearer frequency wherein the second bearer frequency is orthogonal to the first bearer frequency, and wherein the preamble comprises a data pulse sequence followed by a Barker sequence; this pulse of Barker data and sequence are separated by a transmission time period equivalent to the transmission period of at least one binary symbol.

14. A burst mode transmitter of claim 13, wherein the Barker sequence has a length of at least thirteen bits.

15. A burst mode transmitter of claim 14, wherein the Barker sequence comprises a thirteen-bit word code.