Coded data generation or conversion – Digital code to digital code converters – Adaptive coding
Reexamination Certificate
1999-01-21
2001-08-07
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
Adaptive coding
C370S342000
Reexamination Certificate
active
06271772
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of European Patent Application No. 98300556.2, which was filed on Jan. 27, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to iterative decoding of signals in a Multiuser Detection and Demodulation System (MDDS), e.g. a base station in a digital wireless communication system.
2. Description of the Related Art
Recent improvements in communication theory (using the “Turbo Principle”) have shown that in certain digital communication systems, involving a plurality of users in wireless communication with a receiver, an improvement in the quality of the decoded signal can be achieved by applying iterative decoding steps to the received data. In particular, “Iterative Equalization and Decoding in Mobile Communication Systems” by Bauch, Khorram and Hagenauer, EPMCC '97, pp 307-312, October 1997, Bonn, Germany, discusses the application of the Turbo principle to iterative decoding of coded data transmitted over a mobile radio channel. In order to be suitable for iterative decoding, a transmitted signal must be encoded by at least two concatenated codes, either serially or parallely concatenated.
The signal is then decoded in a first decoding step, a first decoder being used to decode the inner code and a second decoder is used to decode the outer code, to provide soft output values on the reliability of the hard decision values. In a first iteration the decoding step is repeated and the soft output values are used as input values for the first and second decoder.
In the particular application of a mobile communication system, the channel encoder and the intersymbol interference (ISI)-channel may be viewed as a serially concatenated encoding scheme, with the channel encoder acting as the outer encoder and the ISI-channel acting as an inner, rate 1, block encoder. Thus, iterative decoding is suitable for application, in particular, to the European Wireless Digital Cellular Standard “GSM” with the equalizer performing the inner decoding step and the decoder providing the outer decoding step. Where bad communication channel conditions (low SNR, fading, multipath propagation, etc) exist, an improvement in the Bit Error Rate (BER) may be achieved with each iterative decoding step until a BER floor is reached. The signal received by a base station is equalized to provide soft decision values of the received coded bits.
Repeating the decoding step several times can improve the BER of the received signal. However, each iterative decoding step consumes resources, such as memory, computation time and ties up dedicated ASICs (Application Specific Integrated Circuits). In a practical base station, the number of signals that can be decoded in parallel is limited by the number of signal processing units (SPU) available; providing iterative decoding hardware, such as digital signal processors (DSPs), and software to each SPU adds considerably to the cost and complexity of the base station.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided apparatus for iteratively decoding a signal comprising:
a signal processing unit; and
iterative decoding resources for running at least one iterative decoding process on said signal
characterized in that the iterative decoding resources are located in a central pool and are allocated to said signal process unit when an iterative decoding process is required.
Each user in a MDDS may have a different Quality of Service (QoS) requirement, i.e. different BER and latency constraints due to differing communication services. For example: voice communication has the lowest BER requirement (i.e. can tolerate many bit errors) with the highest latency constraints (i.e. cannot tolerate long delays in two way conversation); visual communication has a higher BER requirement and high latency constraints; data communication (e.g. wireless Internet web-browsing) has the highest BER requirements and the lowest latency constraints. Each user communicates with the base station with a different signal quality (i.e. SNR), multipath propagation and fading due to differing distance from the base station, propagation environment and, if mobile, speed.
An advantage of the invention is that for each user a differing number of iterative decoding steps may be performed to achieve a target QoS requirement.
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Bauch, et al “Iterative Equalization and Decoding in Mobile Communications Systems” EPCMCC '97, The Second European Personal Mobile Communications Conference Together With 3. ITG-Fachtagung “Mobile Kommunikation” Sep. 30-Oct. 2, 1997 Berlin pp. 307-312.
European Search Report dated Apr. 14, 1998.
Brink Stephan ten
Luschi Carlo
Mujtaba Syed Aon
Sandell Magnus
Strauch Paul Edward
Lucent Technologies - Inc.
Wamsley Patrick
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