International Business Machines Corporation

Other

Philippe Emmanuel Thirion

Dominique N Godard

Andre E Desblache

Karl F Osterlund

Thomas E Stern

Gottfried Ungerbock

Jean Cholat-Namy

Roland E Kuhne

Simon Huon

Stephen Eugene Morrow

Gabriel I Epenoy

Bernard P Laurent

Lawrence E Rosen

Hans-Peter Kaser

A digital modem is connected to a CBX in a network. Data is transmitted to the digital modem in a data field of synchronous serial data frames. The digital modem converts the data into a digital signal corresponding to a time sampled analog signal representing the data. The converted digital signal is communicated to a digital to analog converter for transmission on a telephone line. Analog signals received on the telephone line are digitized, and then converted to data in the digital modem.

Digital modem

A method of testing a communication network that comprises a first and a second multiport modem communicating with each other through a transmission channel, each of said modems being provided with a number of input/output interfaces and each of the interfaces on either modem being associated with a corresponding interface on the other modem. In accordance with the method of the present invention, a test request is applied to one of the interfaces on the first multiport modem, which responds thereto by generating a test configuration code identifying that interface. This modem is then caused to assume a so-called test configuration, in which only that interface to which the test request was applied is active, and a test command comprising an indication of the test to be performed and a link level identifier is applied to that interface. If the identifier designates the link level to which the first modem belongs, this modem will control the test specified in the test command. If another link level is designated, then the test command and the test configuration code will both be sent to the second multiport modem. The second modem will then decode the link level identifier and, if the link level so designated is not the one to which it pertains, will assume a test configuration such that only the interface associated with the first modem interface which received the test request will be active, and the test command will be applied to that active interface. In accordance with another aspect of the invention the test configuration code also identifies the bit rate associated with the test command. The invention also provides a test system that implements the above method. The invention further provides an improved multiport modem to be used in conjunction with the test method and system mentioned above.

Multiport modem and the use thereof in a method and a system for testing

A method and a device for training the equalizer of a receiver used in a QAM transmission system, by means of an unknown data signal, thereby enabling in particular said equalizer to be trained in the cases described above. In accordance with the method of the present invention, in a data receiver wherein, under normal operating conditions, the data is detected with respect to a first constellation, the equalizer is trained by detecting the data with respect to a second constellation which comprises fewer points than said first constellation and by adjusting the coefficients of the equalizer by means of an error signal produced as a result of the detection operation performed with respect to the second constellation. In accordance with a first embodiment of the present invention, the second constellation is comprised of those points of the first constellation that are farthest from its center. In accordance with a second embodiment of the invention, the points of the second constellation are obtained as follows: the first constellation is divided into L sets of points S.sup.l, l=1, 2, . . . , L and a point b.sup.l of the second constellation is associated with each set S.sup.l in accordance with the relation ##EQU1## where the a.sup.k 's are those points of the first constellation that belong to the set S.sup.l.

Method and device for training an adaptive equalizer by means of an

A specialized processor capable of computing a sum of products S=.SIGMA..+-.Pi where every product Pi is the product of two n-bit complex operands Ai+j Bi, the multiplier, and Ci+j Di, the multiplicand, where j=.sqroot.-1. The processor includes an instruction storage, means for decoding instructions read out of said storage and for controlling the operation of the processor, a data storage, and a multiplication and accumulation unit which has two multiplier-accumulator devices and several buffers for storing the operands Ai, Bi, Ci and Di sequentially read out of data storage. The real part Ai and the imaginary part Bi of the multiplier are respectively applied to the Multiplier inputs of the multiplier-accumulator devices and the real part Ci of the multiplicand is applied to the Multiplicand inputs of the multiplier-accumulator devices, which simultaneously compute the products Ai Ci and Bi Ci. The imaginary part Di of the multiplicand is then applied to the Multiplicand inputs of the multiplier-accumulator devices. The first of these then computes the product Bi Di and adds the same to the product Ai Ci, while the second device computes the product Ai Di and adds the same to the product Bi Ci to simultaneously provide the real and imaginary parts of the product Pi.

Specialized microprocessor for computing the sum of products of two

In a receiver for PSK modulated signals, carrier phase tracking is achieved by a feedback loop comprising a phase error predictor. Means are provided for adaptively setting the gain factor in the phase error predictor to an optimum value, in response to successive residual phase errors.

Arrangement for compensating carrier phase errors in a receiver for

A statistical data detection method for use in a synchronous data transmission system employing either phase modulation, combined amplitude and phase modulation or quadrature amplitude modulation. The signal space diagram of the possible states of the transmitted signal and their influence zones is divided into N elementary squares. Since the squares are rather coarse to save storage space, many such squares belong to more than one influence zone. The influence zone of a state Z defines the region within which the received signal, P, will lie when state Z has been transmitted. A word in a ROM is assigned to each elementary square, and each word comprises two entries. The entries are identical when a square falls wholly within a single influence zone. Otherwise, the entries are different. Parts of the received signal are converted into an address for addressing the ROM. If the two entries of the word read from the ROM are identical, detection is completed, the transmitted state is the state represented by the entries. If the two entries are different, however, signifying two different states, the square of the distance between P and each of the two states is computed. The closer state is indicated as the most probable transmitted state.

Statistical data detection method and apparatus

A digital phase filter including two decision filters connected in cascade or parallel for minimizing the noise components in a received phase modulated digital signal. The first decision filter cancels the residual noise component representing the phase intercept component and the phase shift component introduced by frequency shift, and the second decision filter minimizes the random noise component representing phase jitter and white noise.

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St-Paul-de-Vence, France

Philippe Emmanuel Thirion