408 research outputs found
Multilevel Coded Modulation for Unequal Error Protection and Multistage Decoding—Part II: Asymmetric Constellations
In this paper, multilevel coded asymmetric modulation with multistage decoding and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings are more promising than traditional (Ungerboeck-type) partitionings, to achieve UEP capabilities with multilevel coding and multistage decoding. Three types of unconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM constellations over the additive white Gaussian noise channel to introduce design guidelines. Generalizations to other PSK and QAM type constellations follow the same lines. Upper bounds on the bit-error probability based on union bound arguments are first derived. In some cases, these bounds become loose due to the large overlappings of decision regions associated with asymmetric constellations and unconventional partitionings. To overcome this problem, simpler and tighter approximated bounds are derived. Based on these bounds, it is shown that additional refinements can be achieved in the construction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations
Density Evolution for Deterministic Generalized Product Codes with Higher-Order Modulation
Generalized product codes (GPCs) are extensions of product codes (PCs) where
coded bits are protected by two component codes but not necessarily arranged in
a rectangular array. It has recently been shown that there exists a large class
of deterministic GPCs (including, e.g., irregular PCs, half-product codes,
staircase codes, and certain braided codes) for which the asymptotic
performance under iterative bounded-distance decoding over the binary erasure
channel (BEC) can be rigorously characterized in terms of a density evolution
analysis. In this paper, the analysis is extended to the case where
transmission takes place over parallel BECs with different erasure
probabilities. We use this model to predict the code performance in a coded
modulation setup with higher-order signal constellations. We also discuss the
design of the bit mapper that determines the allocation of the coded bits to
the modulation bits of the signal constellation.Comment: invited and accepted paper for the special session "Recent Advances
in Coding for Higher Order Modulation" at the International Symposium on
Turbo Codes & Iterative Information Processing, Brest, France, 201
Multiresolution MBMS transmissions for MIMO UTRA LTE systems
Hierarchical constellations constitute a simple technique for achieving multiresolution and, therefore, are appealing for MBMS (Multimedia Broadcast and Multicast Service). In this paper we consider the use of M-QAM hierarchical constellations (Quadrature Amplitude Modulation) combined with MIMO (Multiple Input Multiple Output) for the transmission of multicast and broadcast services in UTRA (Universal Mobile Telecommunications System Terrestrial Radio Access) Long Term Evolution (LTE) systems based on Orthogonal Frequency Division Multiplexing (OFDM). Due to the demanding channel estimation requirements and the high sensitivity to interference resulting from the usage of several antennas and hierarchical constellations, an enhanced receiver based on the turbo concept is employed and its performance is evaluated.info:eu-repo/semantics/acceptedVersio
Low Complexity Rate Compatible Puncturing Patterns Design for LDPC Codes
In contemporary digital communications design, two major challenges should be addressed: adaptability and flexibility. The system should be capable of flexible and efficient use of all available spectrums and should be adaptable to provide efficient support for the diverse set of service characteristics. These needs imply the necessity of limit-achieving and flexible channel coding techniques, to improve system reliability. Low Density Parity Check (LDPC) codes fit such requirements well, since they are capacity-achieving. Moreover, through puncturing, allowing the adaption of the coding rate to different channel conditions with a single encoder/decoder pair, adaptability and flexibility can be obtained at a low computational cost.In this paper, the design of rate-compatible puncturing patterns for LDPCs is addressed. We use a previously defined formal analysis of a class of punctured LDPC codes through their equivalent parity check matrices. We address a new design criterion for the puncturing patterns using a simplified analysis of the decoding belief propagation algorithm, i.e., considering a Gaussian approximation for message densities under density evolution, and a simple algorithmic method, recently defined by the Authors, to estimate the threshold for regular and irregular LDPC codes on memoryless binary-input continuous-output Additive White Gaussian Noise (AWGN) channels
On BICM receivers for TCM transmission
Recent results have shown that the performance of bit-interleaved coded
modulation (BICM) using convolutional codes in nonfading channels can be
significantly improved when the interleaver takes a trivial form (BICM-T),
i.e., when it does not interleave the bits at all. In this paper, we give a
formal explanation for these results and show that BICM-T is in fact the
combination of a TCM transmitter and a BICM receiver. To predict the
performance of BICM-T, a new type of distance spectrum for convolutional codes
is introduced, analytical bounds based on this spectrum are developed, and
asymptotic approximations are also presented. It is shown that the minimum
distance of the code is not the relevant optimization criterion for BICM-T.
Optimal convolutional codes for different constrain lengths are tabulated and
asymptotic gains of about 2 dB are obtained. These gains are found to be the
same as those obtained by Ungerboeck's one-dimensional trellis coded modulation
(1D-TCM), and therefore, in nonfading channels, BICM-T is shown to be
asymptotically as good as 1D-TCM.Comment: Submitted to the IEEE Transactions on Communication
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