Abstract: A rate controller in a transcoder, which receives a stream of compressed frames carried in a bit stream, selectively determines whether to quantize and/or threshold slices of a frame carried in the stream of frames. The rate controller determines the input size of the frame and based at least in part upon at least a desired size, requantizes and/or thresholds the frame such that the output size of the frame is approximately the desired size.

Abstract: A video coding system and method for coding an input frame in which the evolution of discrete cosine transform (DCT) coefficients is modeled as a Laplace-Markov process, the system comprising: a base layer processing system for generating a base layer reconstruction; an enhancement layer processing system for generating an enhancement layer reconstruction; and an entropy constrained scalar quantizer (ECSQ) system for descritizing a prediction residual between the input frame and an estimation theoretic (ET) prediction output; wherein the ECSQ system utilizes an ECSQ that comprises a uniform threshold quantizer with a deadzone size defined by the equation: ? ? ( ? , t * ) = 2 ? ( 1 1 - ? 2 ? ? t * - 1 ) , where ? ? ? ? ( ? , ? ) = ( ? ? - 1 ) ? exp ? { - ? ? [ d ? ( ? - ? ? ( ? ) ) - d ? ( - ? ) d ? ( ? - ? ? ( ? ) ) - d ? ( - ? ? ( ? ) ) ] } ? .

Abstract: An apparatus and method for selecting a method from a set of methods for transcoding video data, where the data may be transmitted between at least two communication apparatuses via a communication network, the method comprising the steps of determining at least one weighting factor (W1, W2) to attribute to each of the transcoding methods of the set, the at least one weighting factor depending on the data to be transcoded, weighting a mean value of at least one characteristic representative of each of the transcoding methods of the set by applying adapted weighting factors (W1, W2), and selecting a transcoding method as a function of the weighted mean values.

Abstract: An apparatus and method thereof to encode a moving image include a discrete cosine transform (DCT) unit performing a DCT process on input video data, a quantizer, and a motion estimation (ME) unit calculating a motion vector and a SAD per macro block. A DCT computational complexity calculator calculates a computational complexity of the ME unit, estimates a difference between the ME computational complexity and a target ME computational complexity, and updates a target DCT computational complexity based on the estimated difference. A DCT skipping unit sets a threshold value to determine whether to skip performing the DCT process on the input video data, based on the target DCT computational complexity updated by the DCT computational complexity calculator, compares the SAD per macro block, and the quantization parameter with the threshold value, and determines whether to allow the DCT unit to perform the DCT process on the input video data.

Abstract: To provide a process for coding the moving picture with higher speed and enhanced efficiency. The present invention provides a moving picture coding method for coding a moving picture of processing object through a predetermined process including a motion estimating process, determining whether or not the predetermined process (e.g., DCT process and quantization process) for a block of processing object can be omitted on the basis of the information regarding a difference between the block and a reference block of a frame to be referenced in coding (i.e., a frame to be referenced in making the motion vector detection), and a quantization parameter for use in a quantization process of the moving picture, performing the predetermined process if it is determined that the predetermined process can not be omitted, and omitting the predetermined process if it is determined that the predetermined process can be omitted and making a set defined value the result of the predetermined process for the block.

Abstract: An apparatus and method for processing a multimedia digital bitstream is disclosed. The apparatus comprises a processing chain made up of a plurality of media processors. Each media processor processes a portion of the multimedia digital bitstream in real time. Each portion of the multimedia digital bitstream is split into a primary bitstream and a secondary bitstream. The primary bitstream is processed and merged with the unprocessed secondary bitstream. The parallel processing method of the present invention enables the processing chain to output a fully processed bitstream in real time. The processing chain may be used to transcode a high definition (HD) video bitstream in real time using a plurality of bitrate transcoder units.

Abstract: Apparatus and method for adaptively controlling a bit rate of a video transcoder are disclosed. Logarithmic R-Q characteristics obtaining the adaptive R-Q characteristics suitable to characteristics of an inputted image are proposed, and the parameter (?) compensating the difference between the coding efficiency of MPEG-1 and the coding efficiency of MPEG-4 is not fixed as a specific value but changed adaptively according to the characteristics of an image. Accordingly, an accurate quantization parameter of MPEG-4 is generated. Thus, on the basis of the proposed concepts, the bit rate is adaptively controlled when the bit stream of MPEG-1 is converted into a bit stream of MPEG-4, so that the picture quality (PSNR) can be heightened and more accurate output bit rate can be obtained.

Abstract: A method adaptively encodes a video including a sequence of images, where each image is a picture of two fields. Each image is first separated into a top-field and a bottom-field. Motion activity is extracted from the top-field and the bottom-field, and each image is encoded using either frame encoding or field encoding depending on the extracted motion activity.

Abstract: Code quantity control based on a virtual buffer is executed by using information extracted from picture compressed information conforming to a predetermined system. Thus, a reference quantization scale can be held at a fixed value throughout a frame. As a result, it is possible to generate picture compressed information having a smaller code quantity.

Abstract: A variable bit rate (VBR) representation of an image sequence is segmented based on a plurality of time intervals. For each of at least two of the time intervals, the method comprises: determining which of the packets, denoted by Pp, in the VBR representation within the presently-considered time interval has a number of blocks of information per unit time greater than a baseline value; determining which of the packets, denoted by Pn, in the VBR representation within the presently-considered time interval has a number of blocks of information per unit time less than the baseline value; and creating a second representation of the image sequence in which some blocks of information Bp are removed from at least one Pp packet and interlaced with blocks of information in at least one Pn packet to produce reformatted packets.

Abstract: Video encoding methods and video encoders that provide improved performance while reducing power consumption. In one aspect, a video encoding method comprises the steps of outputting a parameter for a slice of a current frame, wherein the slice comprises a plurality of macroblocks, processing the slice by consecutively encoding and decoding each macroblock of the slice in response to the parameter, and outputting an interrupt signal for the slice The parameter preferably comprises an address of the first macroblock of the slice, an address of a search area in a previous frame, the search area corresponding to a current macroblock in a current frame, and a number of macroblocks comprising the slice.

Abstract: A Method And Apparatus For Control of Rate-Distortion Tradeoff by Mode Selection in Video Encoders is Disclosed. The system of the present invention first selects a distortion value D near a desired distortion value. Next, the system determines a quantizer value Q using the selected distortion value D. The system then calculates a Lagrange multiplier lambda using the quantizer value Q. Using the selected Lagrange multiplier lambda and quantizer value Q, the system begins encoding pixelblocks. If the system detects a potential buffer overflow, then the system will increase the Lagrange multiplier lambda. If the Lagrange multiplier lambda exceeds a maximum lambda threshold then the system will increase the quantizer value Q. If the system detects a potential buffer underflow, then the system will decrease the Lagrange multiplier lambda. If the Lagrange multiplier lambda falls below a minimum lambda threshold then the system will decrease the quantizer value Q.

Abstract: An audio encoder regulates quality and bitrate with a control strategy. The strategy includes several features. First, an encoder regulates quantization using quality, minimum bit count, and maximum bit count parameters. Second, an encoder regulates quantization using a noise measure that indicates reliability of a complexity measure. Third, an encoder normalizes a control parameter value according to block size for a variable-size block. Fourth, an encoder uses a bit-count control loop de-linked from a quality control loop. Fifth, an encoder addresses non-monotonicity of quality measurement as a function of quantization level when selecting a quantization level. Sixth, an encoder uses particular interpolation rules to find a quantization level in a quality or bit-count control loop. Seventh, an encoder filters a control parameter value to smooth quality. Eighth, an encoder corrects model bias by adjusting a control parameter value in view of current buffer fullness.

Abstract: An information stream organized as a sequence of blocks is encoded according to a graceful degradation principle. The stream poses temporal non-uniform data processing requirements. In particular, with respect to a received block one or more blockwise defined control parameters and an associated blockwise processing load are detected (44). Under control (46) of a processing load for one or more previous blocks, one or more later blocks before processing thereof get an adjustment (48) of one or more of the control parameters. This lowers an expected load for the later block in case of an excessive load, and vice versa when detecting a sub-standard load.

Abstract: A digital video encoder is presented adapted for dynamically switching between sets of quantizer matrix tables without pausing encoding of a stream of video data. Two or more sets of quantizer matrix tables are held at the encoder's quantization unit and compressed store interface for dynamically switching between sets of quant matrix tables at a picture boundary of the sequence of video data, i.e., without stopping encoding of the sequence of video data. Further, while one set of matrix tables is being employed to quantize the stream of video data, the encoder can be updating or modifying another set of quantization matrix tables, again without stopping encoding of the sequence of video data.

Abstract: A method and apparatus for encoding pictures of a moving pictures sequence according to an overall target bit-rate, such as in a MPEG video encoder. Each picture has an assigned picture coding type for which a quality factor is adaptively determined according to past bit usages, so that bits can be adaptively allocated amongst picture types for optimizing visual quality of the encoded pictures.

Abstract: A picture encoding system conversion device and a code rate conversion device for realizing the conversion taking into account both time delay and picture quality using the information on the code volume of the encoding parameters, input and output buffers and an input bitstream. There are provided a decoder 1 including an input buffer 21, a VLD unit 22, an inverse quantizer 23, an IDCT unit 24, an adder 35, a frame memory 26 and a motion compensation prediction unit 27; an encoder 2 including an adder 31, a DCT unit 32, a quantizer 33, an inverse quantizer 34, an IDCT unit 35, an adder 36, a frame memory unit 37, a motion compensation prediction unit 38, a VLD unit 39 and an output buffer 40; and a transcoder controller 3 including a decoder monitor unit 51, an input buffer monitor unit 52, a reception transmission channel monitor 53, a sending transmission channel monitor 63, an output buffer monitor unit 62 and a quantization step controller 74.

Abstract: An apparatus for partitioning moving picture data comprises a first quantizing unit for first-quantizing a received video signal and outputting a first-quantized signal; and a second quantizing unit for second-quantizing the first-quantized signal and partitioning the first-quantized signal into a preceding part and a succeeding part.

Abstract: Digital signals are transmitted on a bus at given instants selectively in a non-encoded format and an encoded format so as to minimize the switching activity on the bus. Given the same value of switching activity, the decision whether to transmit the signals in non-encoded format or in encoded format is taken according to the choice of maintaining constant, without transitions, the value of the additional signal, which signals that encoding of the signals transmitted each time has taken place or has been omitted.

Abstract: The present invention is related to video encoding. In an embodiment, a bit budget is calculated for a first scene. In addition, bit budgets for corresponding frames, including at least a first frame, within the first scene are determined. Optionally, bit budgets corresponding to macroblocks within the first frame are also determined.

Abstract: A method of producing an output bitstream of coded digital video data with a bit-rate different from the bit-rate of an input bitstream includes dividing the input bitstream into a sequence of coded data and a sequence of control bits. The sequence of control bits is modified as a function of the desired bit-rate of the output bitstream that is different from the bit-rate of the input bitstream. An output sequence of control bits is produced. The method further includes decoding the sequence of coded data producing an intermediate sequence of data, and quantizing with a pre-established step and coding the intermediate sequence of data producing an output sequence of coded data. The output sequences producing the output bitstream are merged with the desired bit-rate.

Abstract: The present invention enables to effectively coding a predetermined time length of a video signal with a variable bit rate at real time (one-path) into a total coding bit amount of a constant data capacity. A coding difficulty calculator 13 determines a coding difficulty of an input signal for each unit time. An allocation bit amount calculator 14 interrelates an allocation sign amount with a coding difficulty for each unit time standardized in advance using an ordinary input signal of the type to which the input signal belongs, so as to obtain a reference value of the allocation sign amount for each unit time interrelated with the coding difficulty supplied from the coding difficulty calculator 13. This reference value of the allocation sign amount is modified by a controller 15 into an actual allocation sign amount, according to which the input signal is coded by a moving picture image coding apparatus 18, so as to create a coded data.

Abstract: An encoding apparatus and method prevents image deterioration generated by repeatedly performing encoding and decoding by using a quantization matrix for quantization which is different from a quantization matrix for inverse quantization. In the encoding apparatus, a matrix selector selects a first quantization matrix in accordance with the complexity of an encoded picture pattern, and supplies a quantizer with information on the selected first quantization matrix. A matrix unit rewrites, by information on a second quantization matrix, the information described in an encoded stream output from a variable length code unit so that a quantization matrix to be used for inverse quantization is a second quantization matrix different from the first quantization matrix.

Abstract: A process of bit rate control includes asymmetrical reactions to changes in the signal density of the digital video signals. In the process, two different averaging periods are employed to meet a long term bit rate target and to achieve a short term quick reaction. When encoding a motion picture, the bit rate control is relaxed during high motion scenes to allow high peaks of bit rate at those points. The coding process reacts slowly to transitions from low to high motion sequences to preserve the best overall video quality, and reacts quickly to transitions from high to low motion sequences to enhance the image quality.

Abstract: A method and apparatus for temporally allocating bits between frames in a coding system such that temporal fluctuations are smoothed out. Namely, a picture quality is monitored on a frame by frame basis. An average distortion measure is derived from previous picture frames and that average is compared to the distortion measure of a current frame, where the result is used to effect bit budget allocation for each frame in an input image sequence.

Abstract: A method of determining a quantization parameter for video compression. A block characteristic for blocks in a video frame is quantized and then used to obtain a candidate quantization parameter. With the candidate quantization parameter, a number of bits for the blocks in the video frame is summed, producing a candidate bit rate. If the candidate bit rate is greater than a predetermined bit rate threshold, the candidate quantization parameter is set as the quantization parameter.

Abstract: A video code processing method includes (a), (b), (c) and (d). The (a) step includes providing a first original bit stream including a video code which is a digitized video signal. The (b) step includes generating a second original bit stream at a first timing by delaying the first original bit stream by a specific time interval. The (c) step includes generating a converted bit stream at a second timing. The first original bit stream is code-converted into the converted bit stream. The (d) step includes switching between the second original bit stream and the converted bit stream to output. The specific time interval is adjusted such that the first timing is substantially equal to the second timing.

Abstract: Possible overflow of a video buffer verifier (VBV) buffer employed in MPEG-like video encoders is prevented by controlling bits being drained from a video encoder buffer (eBuff). Specifically, a number of bits in the encoder buffer is determined when a last prior picture (pic n?1) ends, or when it should end. This number of bits (maxBits) is the maximum number of bits to be read from the encoder buffer and written to the remote decoder before a prescribed time T(n). When maxBits has been read from the encoder buffer and written to the decoder, the writing of bits to the remote decoder is stopped until the process is reset. If the prior picture ends early, maxBits is defined as being the number of bits in the encoder buffer at an expected time (Texp) that the picture should have ended less the number of bits written into the encoder buffer between the time the prior picture actually ended and the expected time for it to end, i.e., Texp. If the prior picture is late, i.e.

Abstract: This method and apparatus described herein imposes masking factors to the determined quantization step sizes of macroblocks of a video sequence such that encoding efficiency is increased. A conditional masking method can be used to take advantage of the fact that P-pictures are more important than B-pictures in terms of motion and scene updates as coding noise in such updates are likely propagated by P-pictures. The masking can be applied conditionally to motion/scene update regions of a picture such that coding noise is reduced and therefore bits are saved from less propagation of this noise. Before encoding each macroblock of a picture from an input video sequence, a video encoder with conditional masking determines if the macroblock type belongs to a significant motion or scene update region. A conditional masking factor is then determined for the macroblock based on the determined macroblock type and the picture coding type.

Abstract: As the video signals of macroblocks are coded, they are stored in a buffer. When the total code length of the stored macroblocks exceeds a predetermined value, all but the most recently coded macroblock are output from the buffer as a video packet, and the most recently coded macroblock is coded again. To minimize this occurrence, when each coded macroblock is stored, the code length of the next macroblock is predicted and added to the total length, and if the resulting sum exceeds the predetermined value, all of the coded macroblocks stored in the buffer are output as a video packet.

Abstract: A method and apparatus is provided for estimating the number of bits output from a video coder given a known spatial data content, G={g1, . . . , gN}, of a group of luminance and chrominance blocks, and a known coding mode, d, where d represents the index of said coding mode.

Abstract: To improve qualities of audio and picture signals by distributing adaptively the code quantities of audio codes and picture codes and by adopting variable rate audio coding. The audio/picture processing apparatus handles audio presence information, audio characteristics information, audio quality information, picture quality information, code quantity distribution information, and line capacity information. A code quantity control means decides the distribution of the audio and picture codes, an audio coding format, and a coding rate, whereby the audio signal and picture signal are coded by a picture encoder and an audio encoder. The outputs from the picture encoder and the audio encoder are multiplexed by a multiplexer in order to transmit a multiplexed bit stream onto the network.

Abstract: A method and system for determining and recording a minimal ending video buffer verifier fullness at each of a plurality of entry points in a compressed variable bit rate video bit stream.

Abstract: A rate controller in a transcoder, which receives a stream of compressed frames carried in a bit stream, selectively determines whether to quantize and/or threshold slices of a frame carried in the stream of frames. The rate controller determines the input size of the frame and based at least in part upon at least a desired size, requantizes and/or thresholds the frame such that the output size of the frame is approximately the desired size.

Abstract: A picture information conversion method and apparatus in which, if the compressed picture information with a variable or non-recognized information volume is input, optimum compression processing on the compressed picture information is performed to prevent underflow and/or overflow to suppress deterioration of the picture quality. A compressed information analysis device 3 analyzes the structure of the picture type of the GOP of the compressed picture information input to the FF buffer 2. A bit allocation device 5 generates a pseudo GOP of the input compressed picture information, based on N frames stored in the FF buffer 2 and on the analysis result information stored in the information buffer 4, and allocates a pre-set code volume to respective pictures of the generated GOP so that the output compressed picture information will be at a second bitrate.

Abstract: In a video signal encoding and recording apparatus, a video signal is quantized into a quantization-resultant signal in response to a variable quantization scale. The quantization-resultant signal is recorded on a recording medium. The quantization scale is controlled in response to an encoding rate. The quantization scale is limited to within a range determined by a limit quantization scale. A remaining record capacity of the recording medium is measured. A remaining record time is measured. The encoding rate and the limit quantization scale are updated in response to the measured remaining record capacity and the measured remaining record time.

Abstract: The present invention provides a quantization control system for video coding, for optimizing bit allocation based on visual priority which expresses at high precision human visual characteristics for videos, thereby improving subjective image quality of the whole image even with a limited number of bits.

Abstract: A moving image coding apparatus has a blocking unit for dividing an image applied in units of frames into a plurality of blocks, a mode selection unit for selectively performing intra-frame coding for performing coding within the same frame, and inter-frame prediction coding for performing coding between frames, for each of the plurality of blocks, a self-image display unit for displaying the image, and a qualitative refresh map creation unit for creating a refresh map which sets a shorter refresh period for a block corresponding to a predetermined area on a display screen of the display means than the rest of the plurality of blocks. The mode selection unit performs the intra-frame coding at the refresh period set in the refresh map.

Abstract: An image encoder of the present invention includes an encoder unit for generating first encoded data, re-encoder unit for re-encoding the first encoded data to generate second encoded data, parameter updating unit for updating of the encoder unit when the sum of data amount of the first and second encoded data reaches a target amount, and controller for starting a re-encoding process when the sum reaches the target amount. The encoder unit encodes still unencoded image data using all encoding parameters that are updated from the parameter that has been used at the beginning of the encoding of the source image data. The image encoder thus encodes image data into data having a desired data amount on a substantial real-time basis. When the encoded data is decoded, non-uniformity in image quality of the decoded image due to different numbers of encoding and decoding operations is controlled.

Abstract: A variable bit rate (VBR) representation of an image sequence is segmented based on a plurality of time intervals. For each of at least two of the time intervals, the method comprises: determining which of the packets, denoted by Pp, in the VBR representation within the presently-considered time interval has a number of blocks of information per unit time greater than a baseline value; determining which of the packets, denoted by Pn, in the VBR representation within the presently-considered time interval has a number of blocks of information per unit time less than the baseline value; and creating a second representation of the image sequence in which some blocks of information Bp are removed from at least one Pp packet and interlaced with blocks of information in at least one Pn packet to produce reformatted packets.

Abstract: A residue code amount is calculated. A threshold act_thrsh corresponding to the residue code amount is obtained. A variable mb that designates a macro block is initialized to zero. The variable mb is compared with the total number of macro blocks. When the variable mb matches the total number of macro blocks, the process is completed. Otherwise, the rank of the activity information of the macro block designated by the variable mb is compared with the rank of the threshold act_thrsh. When the rank of the activity information is lower than the rank of the threshold act_thrsh, since there is a possibility of which q_scale can be decreased, q_scale is calculated with the activity information of the macro block mb and min_qq. q_scale of the macro block is subtracted from the total code amount. The subtracted resultant data is stored in a variable tmp. Thereafter, the variable tmp is compared with a target code amount GEN_TGT.

Abstract: An image information coding apparatus codes an input image signal in a manner optimized on the basis of the visual characteristics. In quantization, an input image signal is divided into blocks, an orthogonal transform is performed on a block-by-block basis, and resultant orthogonal transform coefficients are quantized. A quantizer includes a weighter for, in the quantization, performing weighting on each component of the orthogonal transform coefficients by means of an addition operation on a parameter specifying one of elements of a series of numbers arranged in accordance with a predetermined rule in correspondence with quantization step sizes.

Abstract: Input moving pictures are encoded with motion-compensated prediction. Detected first is an mount of codes generated for each encoded picture of the input moving pictures. Detected next is an average quantization scale factor of quantization scale factors used for quantizing the pictures of the input moving pictures when encoded. Also detected is picture characteristics of at least the input moving pictures. Complexity of each picture is calculated in response to the mount of codes generated for each picture, the average quantization scale factor and the picture characteristics. An amount of codes to be allocated to a present picture to be encoded is decided in response to the mount of codes generated for each picture, picture characteristics and the complexity of each picture, for obtaining a quantization scale factor for the present picture.

Abstract: A method and system of regulating the computation load of an MPEG encoder in a video processing system are provided. A stream of data blocks is received and buffered temporarily for subsequent retrieval during an encoding mode. The buffered data block is then retrieved from the buffer for an encoding operation in accordance with a conventional encoding method. Meanwhile, the fullness level of the buffer is monitored to determine an appropriate encoding complexity for a subsequent encoding process. To this end, a predetermine threshold range is compared to the fullness level so that the subsequent encoding operation can be performed at an improved buffer efficiency.

Abstract: In order to enhance the picture quality of a detected area, the present invention provides a video coding apparatus. In the apparatus, a reliability indicative of the degree of coincidence of an area detected by an important area detecting section with a real important area is calculated, and a coding parameter calculating section calculates a coding parameter to be set to the detected area according to the reliability, thereby controlling the picture quality of the detected area. Consequently, a whole image has a coding bit amount which does not break the restrictions of a transmission bit rate, and a larger coding bit amount is assigned to the important area so that a picture quality thereof can be improved and a visibility can be enhanced. In addition, the picture quality is more enhanced if a probability that the detected area might be an important area is higher.

Abstract: A data compressing circuit to compress an amount of data which is stored into an image memory is provided at the front stage of the image memory which is used for a motion compensation prediction. A data decompressing circuit to return the compression data read out from the image memory to the original data is provided at the post stage of the image memory. Since the image data is compressed when reference image data is stored into the image memory which is used for motion compensation prediction, a capacity of the image memory is reduced. In this instance, since the compression of the image data is independently performed on a unit basis of a DCT block layer, it can be matched with a DCT block and successive processes can be performed.

Abstract: Embodiments of the present invention comprise systems and methods for dequantization and inverse transformation of data related to video wherein reduced bit depth intermediate calculations are enabled.

Abstract: To allow an individual picture (1) which comprises picture values (3) grouped together into blocks (2) to be quickly compressed with good picture quality, the picture values (3) are quantized block by block by a quantization factor, with the data volume represented by quantized picture values (3) dropping as the quantization factor rises. After the picture values (3) in a block (2) have been quantized, an actual data volume is determined which corresponds to that data volume represented by the last block (2) quantized which is related to the number of picture values (3) in the last block (2) quantized, and a target data volume is determined which corresponds to that volume of storage space which is available for the picture values (3) still to be quantized and which is related to the number of picture values (3) still to be quantized. If the actual data volume is larger than the target data volume the quantization factor is raised, and vice versa.

Abstract: A multimedia data decoding apparatus to decode multimedia data and method thereof includes a data information extracting unit extracting detail information from the multimedia data. An input buffering unit stores the multimedia data for a predetermined time. A decoding unit decodes the multimedia data from the input buffering unit into original signals of respective types. An output buffering unit stores the decoded multimedia data for a predetermined time. A control unit determines buffering capacities of the input buffering unit and the output buffering unit based on the detail information extracted by the data information extracting unit.

Abstract: In a transmission system for digital symbols, such as used for DVB, source symbols are encoded by a block coder (4), subjected to an interleaving operation in an interleaver and subsequently encoder in a channel encoder (8) according to one out of a plurality of possible channel codes. The output symbols of the channel encoder (8) are applied to transmit means (10). These output symbols are modulated on a carrier and applied to an antenna (12). An antenna (14) connected to a receiver (16) receives the signal transmitted by the antenna (12). Receive means (18) are arranged for amplifying and demodulating the signal received from the antenna (14). The output of the receive means (18) are applied to quantizing means (20) which convert its input signal into a quantized digital signal, before applying it to a Viterbi decoder 22. The complexity of the Viterbi decoder 22 depends on the number of quantization levels at the output of the quantization means (20).