DATA COMMUNICATIONS SYSTEM AND METHOD OF DATA TRANSMISSION

A 1553 data communication system having a primary data bus, a redundant data bus and a non-1553 data communication overlay system is provided. The non-1553 data communication overlay system comprises a non-1553 bus controller terminal and a non-1553 remote terminal. Each non-1553 terminal includes a non-1553 transmitter block connected to the primary bus and the redundant bus for sending non-1553 signals, a non-1553 receiver block for receiving non-1553 signals and a non-1553 receive path selection block. The non-1553 receive path selection block selectively establishes a receive path between the primary data bus or the redundant data bus and the non-1553 receiver block according to predefined receive path selection criteria. A 1553 data communication method is also provided.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made now toFIG. 1, illustrating a 1553 communication system10according to the invention. System10comprises a primary data bus20and a redundant data bus30, a Bus Controller (BC) terminal100and a plurality of Remote Terminals (RT)110,111,112. 1553 compatible devices are in most cases analog, so in general, each of the Remote Terminals includes a transceiver which converts the binary bit streams on buses20,30to analog signals. The Remote Terminals also comprise encoder/decoder equipment and protocol controllers, as well as other necessary components to interface to any higher layer sub-systems. The Bus Controller100is a terminal consisting of a superset of the capabilities of the Remote Terminals110,111,112, acting as the media access controller (MAC) to the buses20,30, utilizing a command/response protocol. In embodiments of the invention operable in accordance with the 1553 standard, only the Bus Controller100can issue a command on the buses while Remote Terminals only respond to a command received from the Bus Controller100.

Within the 1553 communication systems10, Remote Terminal110,112are capable of sending and receiving 1553 signals over the primary and redundant buses20,30, whereas Remote Terminal111is capable of sending and receiving non-1553 signals. Furthermore, BC100is capable of sending both 1553 and non-1553 signals. 1553 signals are defined herein as signals in accordance with 1553 standard signaling schemes, including but not limited to primitive Manchester II bi-phase signaling. Non-1553 signals are any signals that can be differentiated from 1553 signals either in frequency domain, time domain, Laplace domain, or by any other method obvious in the art. Non-1553 signals must be generated so as to enable co-propagation with 1553 signals through an existing 1553 system along the primary and secondary buses20,30. Preferably, when co-propagating non-1553 signals, impact to the transmission of the 1553 signals is minimal. Without limitation, Digital Subscriber Line (DSL) code gain methods such as Carrier-less Amplitude/Phase (CAP) coding and Orthogonal Frequency Division Multiplexing (OFDM), closely related to Discrete Multi-Tone (DMT) coding are particular examples of possible non-1553 signals.

Terminals capable of either sending or receiving non-1553 signals, such as111, are defined herein as non-1553 terminals or non-1553 communication devices. Likewise, terminals capable of receiving 1553 signals, such as110and112, are defined herein as 1553 terminals or 1553 communication devices. It will be recognized by those skilled in the art that 1553 terminals and non-1553 terminals as defined herein are differentiated by their functionality and signaling capabilities, but their implementation may take various forms. Physically, they might be integrated on the same IC or be built on different boards, but also they might occur at different physical locations, all according to requirements of the communication system and to manufacturing preferences. In an alternate embodiment, two distinct BC terminals, one controlling 1553 RT's and the other controlling the non-1553 RT's, might be provided.

Referring now toFIG. 2, a non-1553 terminal111according to an embodiment of the invention is illustrated. The non-1553 terminal111comprises a non-1553 transmitter block40connected to the primary bus20and the redundant bus30of a 1553 communication system, for sending non-1553 signals on these buses. The non-1553 terminal111also comprises a non-1553 receiver block50for receiving non-1553 signals via a receive path to be established with one of the primary bus20and the redundant bus30, by a non-1553 Receive Path Selection block60. As it will be recognized by someone skilled in the art, the non-1553 Receive Path Selection block60comprises means for selecting one of the data buses based on a predefined receive path selection criteria, as well as means for establishing a connection, such as, but not limited to, an electrical connection, between the selected bus and the non-1553 receiver block50. Predefined receive path selection criteria of selecting a non-1553 receive path are defined herein as any design criteria aimed at indicating the appropriate receive path, from a plurality of data buses to a non-1553 receiver.

FIG. 3illustrates the flowchart of a method of receiving non-1553 signals within the 1553 communications system10, according to an embodiment of the invention. According to this embodiment, the method comprises the step of monitoring the performance of the primary bus20and of the redundant bus30, as shown at61. Preferably, the monitoring step is performed periodically, based on metrics that may include, without limitation, Signal to Noise Ratio (SNR), Bit Error Rate (BER), channel capacity etc. Based on the values obtained during the monitoring step, preferably averaged over appropriate time intervals, a selection of an appropriate receive path, from the primary bus to the receiver or from the redundant path to the receiver, as shown at62, is made. Finally, once a receive path is selected, the connection between the corresponding bus and the non-1553 receiver is established, step63, allowing for non-1553 signals to be received at the non-1553 receiver50.

According to a preferred embodiment, the higher performance bus will be selected as the bus from which to receive signals. For example, under no-bus fault conditions, 1553 signals might be transmitted on the primary bus, leaving the redundant bus available for unfettered transmission of non-1553 signals. When the same bus must be used for both 1553 and non-1553 signals, a multiplexing scheme such as Time Division Multiplexing might be used, although this may not be necessary.

FIG. 4illustrates a 1553b communications system12according to a preferred embodiment of the invention. The 1553b communication system12is built and operates in accordance to the 1553b standard. The 1553b communication system12comprises a primary bus (Bus A)21and a redundant bus (Bus B)31, a 1553b Bus Controller (BC)101and a plurality of 1553b Remote Terminals (RT)115,117exchanging 1553b signals along buses21,31. In addition, the 1553b system12comprises an OFDM Bus Controller102and a plurality of OFDM Remote Terminals114,116.

Each 1553b terminal comprises a 1553b Transmitter70, connecting via a switch to either the primary bus21or the redundant bus31, and a couple of 1553b receivers81,82. Each OFDM terminal comprises an OFDM Transmitter42, connected to the primary bus21and to the redundant bus31, and an OFDM receiver52that can connect via a switch to either bus.

FIG. 5shows a detailed block diagram of a 1553b terminal in the 1553b system12. The 1553b transmitter70comprises a controller block, an encoder, and an analog front end (AFE) block, containing all the circuitry for filtering, for converting the signal from digital to analog and for coupling the signal to the primary bus (Bus A) or the redundant bus (Bus B) via a switch. Each 1553b receiver81,82comprises an AFE block performing necessary filtering and conversion from analog to digital, a decoder block, and a controller block.

FIG. 6illustrates an OFDM terminal according to a preferred embodiment of the invention. The OFDM Transmitter42includes a forward error correction (FEC) unit A for adding FEC bits to an input data bit stream. Forward Error Correction (FEC) may consist of Reed-Solomon, convolutional or other types of coding schemes that will be recognized by someone skilled in the art. The FEC unit A is followed by a mapping block B which maps the encoded bits to frequency domain sub-carriers, which are then transformed to a time domain digital signal (symbol) by an inverse Fast Fourier Transform (IFFT) unit C, which will be recognized by those skilled in the art as means for an efficient implementation of the inverse discrete Fourier Transform (DFT) algorithm. Preferably, the number of bits that are allocated to particular tones is chosen to match the signal to noise conditions of the channel.

The symbols are then received by a preamble unit D, which pre-pends to them a preamble, consisting of a number of synchronization symbols. The preamble allows for synchronization of the transmitted waveform at the receiver, as well as to enable analog gain control (AGC) and channel response estimation. Furthermore, a cyclic prefix is also usually added to the OFDM symbols. Next, the symbols are appropriately shaped by a symbol shaper E before conversion to an analog signal by the analog front end (AFE) F. The symbol shaping may include operations such as widowing and filtering. Following, the OFDM symbols represented as digital signals are converted to analog signals by the analog front end (AFE) F, comprising a digital to analog converter and appropriate analog filters. The AFE may further include an IF/RF mixing stage to convert the signal to higher frequencies.

The OFDM Receiver52selects the analog signal from the primary bus21or redundant bus31, as discussed above. Then, the appropriate RF/IF stages are used to convert the signal to a baseband signal which is then filtered and converted from the analog domain to a digital signal by an analog front end (AFE) which includes an analog to digital converter P. An Automatic Gain Control block (AGC) O controls the input signal level based on power metrics estimated from the synchronization symbols. A Fast Fourier Transform (FFT) is applied to the sampled signal by an FFT block N, preferably with the timing of the FFT based on the detection and timing estimation of the synchronization symbols performed by a Detection Synchronization block S. Channel estimation is achieved based on the synchronization symbols and is used by a De-Modulator M to remove phase and amplitude distortion effects of the channel. Channel equalization is next performed in the frequency domain. A De-Mapping function L converts the demodulated frequency domain sub-carriers to coded data bits, followed by the corresponding forward error correction block R to correct any bit errors (if correctable). The decoded data bits are passed to higher communications layers.

According to the preferred embodiment of the invention, OFDM modulation is used to better utilize the available bandwidth on the bus, creating an “overlay” network to operate concurrently and without disturbing existing 1553b communications. This is accomplished by utilizing OFDM signals with little energy (low PSD) in a 1553b high-energy frequency band and with a relatively constant Power Spectral Density (PSD) in 1553b low-energy frequency band.FIG. 7is a theoretical representation of the PSD of a transmitted OFDM signal relative to a 1553b transmitted waveform. As illustrated, the OFDM waveforms are configured to utilize the frequency band from 5 to 35 MHz where 1553b side lobes of a given 1553b system are relatively low. In addition, the OFDM signals have little energy in the 0 to 5 MHz band. Therefore, interference between OFDM communications and existing 1553b communications is minimized. Alternate embodiments contemplate configuration of OFDM signals with different frequency bands, including an OFDM waveform configured to utilized the frequency band from about 5 MHz to a frequency greater than 35 MHz, such as 40 MHz.

FIG. 8illustrates representative PSD's at a receiver of both a 1553b signal and OFDM signal for a particular bus configuration. In this example, the Signal to Noise Ratio (SNR) has an acceptable level in the frequency band below 5 MHz for a 1553b receiver to decode the 1553b signal. As well, the SNR has an acceptable level in the frequency band above 5 MHz for an OFDM receiver to decode the OFDM signal. It will be understood by those skilled in the art of data communications that the frequency and bandwidth of the OFDM communications devices can be chosen to match the channel conditions of a given 1553b bus to ensure reliable communications for both 1553b and OFDM systems.

When both 1553b and OFDM signals are transmitted on the same bus, relative powers at a receiver would depend on the network topology and the particular locations of transmitters and receivers. A network of this topology and components is generally frequency selective in nature. A transceiver is generally transformer coupled to the bus stub (cable connection to the main bus) and the connecting stubs can be either transformer coupled or direct coupled using isolation resistors only to the main bus.

Referring back toFIG. 4, bus fault design is herein defined as predefined operation of the communication system in the event of bus faults. Examples of bus faults include, without limitation, a broken wire or connector or an issue with a terminal itself. A dual redundant scheme of 1553b communication over system12is as follows: 1553b devices transmit on Bus A under no bus fault conditions and receive from both Bus A and Bus B. Each OFDM device transmits the same signal on both Bus A and Bus B and receives on Bus B under no bus fault conditions. When bus faults occur on Bus A 1553b devices will switch to Bus B for transmission, under BC control. In most 1553b applications, a bus fault is determined on a terminal by terminal basis; however, other bus fault detection designs are not excluded. When the 1553b BC101detects that one of the 1553b RT's does not respond on the primary bus21, it re-sends the command to that RT to transmit on the redundant bus31. Occasionally, the 1553b BC may also send a command on the redundant bus31to test the integrity of the wire.

In order to select a receive path, the OFDM receiver52of the OFDM device114, while connected to the secondary (redundant) bus31, periodically monitors the secondary bus for performance via non-1553 receive path selection unit65. The monitoring is performed based on a predefined design scheme or predefined selection criteria, specifying acceptable performance level for selected metrics. The metrics used for this determination can include but are not limited to SNR, Bit Error Rate and capacity. The metrics could be monitored and averaged over an appropriate time interval. Detection of performance of the redundant bus below acceptable levels, triggers switching the connection of OFDM receiver52from the secondary bus31to the primary bus21, thus establishing an alternate receive path. Switching to the other bus could also be initiated by failing to decode a message on the currently connected bus. Alternately, both buses could be monitored at the same time, and a receive path between the better performing bus and the receiver could be established accordingly, as described earlier in reference toFIG. 3(see step61).

In summary, embodiments of the present invention allow for an overlay of a non-1553 communication scheme over legacy 1553 systems, with minimal impact to the 1553 communications, thereby providing the ability of enhancing the throughput of existent 1553 systems and of adding new digital equipment, without rewiring.

Furthermore, a dual-redundant scheme employing a single non-1553 transmitter and single non-1553 receiver per non-1553 transceiver is presented. Therefore, additional benefits compared to 1553b dual redundancy architecture include lower power, smaller size, less heat dissipation requirements and lower design complexity. It will be obvious to those skilled in the art of data communications that the dual redundant architecture inFIG. 4may scale to more than 2 buses.

Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.