A Two-Stage Capacity-Achieving Demodulation/Decoding Method for Random Matrix Channels

• Published in: IEEE transactions on information theory Vol. 55; no. 1; pp. 136 - 146
• Main Authors: Truhachev, D., Schlegel, C., Krzymien, L.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Capacity achieving; Channels; Code Division Multiple Access; Codes; Coding, codes; Control systems; Decoding; Demodulation; Demodulators; Detection, estimation, filtering, equalization, prediction; Error correction; Exact sciences and technology; Frequency division multiplexing; Information theory; Information, signal and communications theory; Iterative decoding; Matrix; MIMO; Modulation, demodulation; Multiaccess communication; Multiplexers; OFDM; partitioned signaling; Power distribution; random matrix channels; Redundancy; Signal and communications theory; Signal, noise; Telecommunications and information theory; Turbo codes; two-stage decoding; Performance evaluation; Random matrix; Wireless telecommunication; Transmitter; Iterative method; Linear channel; Capacity achieving; Demodulator; Feedforward; MIMO system; Multistage method; Redundancy; partitioned signaling; Turbo code; Decoding; Equalization; two-stage decoding; Concatenation; Intersymbol interference; random matrix channels; Code division multiple access; Orthogonal frequency division multiplexing; Signal processing; Error correcting code; Demodulation
• ISSN: 0018-9448; 1557-9654
• DOI: 10.1109/TIT.2008.2008149

Iterative processing for linear matrix channels, aka turbo equalization, turbo demodulation, or turbo code-division multiple access (CDMA), has traditionally been addressed as the concatenation of conventional error control codes with the linear (matrix) channel. However, in several situations, such as CDMA, multiple-input-multiple-output (MIMO) channels, orthogonal frequency-division multiplexing (OFDM), and intersymbol-interference (ISI) channels, the channel itself either contains inherent signal redundancy or such redundancy can readily be introduced at the transmitter. For such systems, iterative demodulation of the linear channel exploiting this redundancy using simple iterative cancellation demodulators, followed by conventional feedforward error control decoding, provides a low-complexity, but extremely efficient decoding alternative. This two-stage demodulator/decoder outperforms more complex turbo CDMA methods for equal power modes (users). Furthermore, it is shown that arbitrary numbers of modes can be supported if an unequal power distribution is adopted. These power distributions are nested, which means that additional modes can be added without disturbing an existing mode population. The main result shows that these nested power distributions enable the two-stage receiver to approach the Shannon capacity of the channel to within less than one bit for any signal-to-noise ratio (SNR).