This paper discusses a communication system with a multiple-access channel where two users simultaneously send complex-valued signals in the same frequency-band. In this channel, ambiguity in decoding occurs when rece...
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This paper discusses a communication system with a multiple-access channel where two users simultaneously send complex-valued signals in the same frequency-band. In this channel, ambiguity in decoding occurs when receiver trying to estimate each users' signal. In order to solve the ambiguity problem, a family of uniquely decodable code is derived in this paper. The uniquely decodable code is designed by using trellis-coded modulation (TCM) pair where the trellis structure of one TCM is a transformation of the other in the pair. It is theoretically proved that, with the proposed coding scheme, the composite received signal can be uniquely decomposed into the two constituent signals for any power ratio and any phase difference between the received two users' signals. Improvement of BER performance over non-uniquely decodable code is illustrated by computer simulation.
For every natural number n >= 2 and every finite sequence L of natural numbers, we consider the set UDn(L) of all uniquely decodable codes over an n-letter alphabet with the sequence L as the sequence of code word ...
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For every natural number n >= 2 and every finite sequence L of natural numbers, we consider the set UDn(L) of all uniquely decodable codes over an n-letter alphabet with the sequence L as the sequence of code word lengths, as well as its subsets PRn(L)and FDn(L) consisting of, respectively, the prefix codes and the codes with finite delay. We derive the estimation for the quotient vertical bar UDn(L)vertical bar/vertical bar PRn(L)vertical bar, which allows to characterize those sequences L for which the equality PRn(L) = UDn(L) holds. We also characterize those sequences L for which the equality FDn(L) = UDn(L) holds. (C) 2016 Elsevier B.V. All rights reserved.
Multi-user uniquelydecodable (UD) k-ary coding for the multiple-access adder channel is investigated. It is shown that a Tf+g+1-user UD k-ary affine code with code length f+g+1 can be obtained from two T-f-user and T...
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Multi-user uniquelydecodable (UD) k-ary coding for the multiple-access adder channel is investigated. It is shown that a Tf+g+1-user UD k-ary affine code with code length f+g+1 can be obtained from two T-f-user and T-g-user UD k-ary affine codes. This leads to construct recursively a T-n-user UD k-ary affine code with arbitrary code length n. The total rate of the code tends to be higher than those of all the multi-user UD k-ary codes reported previously as the number of users increases.
We investigate the ratio ma of prefix codes to all uniquely decodable codes over an n-letter alphabet and with length distribution L. For any integers n >= 2 and m >= 1, we construct a lower bound and an upper b...
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We investigate the ratio ma of prefix codes to all uniquely decodable codes over an n-letter alphabet and with length distribution L. For any integers n >= 2 and m >= 1, we construct a lower bound and an upper bound for inf(L rho n,L), the infimum taken over all sequences L of length m for which the set of uniquely decodable codes with length distribution L is nonempty. As a result, we obtain that this infimum is always greater than zero. Moreover, for every m >= 1 it tends to I when n -> infinity, and for every n >= 2 it tends to 0 when m -> infinity. In the case m = 2, we also obtain the exact value for this infimum. (C) 2018 Elsevier B.V. All rights reserved.
This paper utilizes uniquely decodable codes[UDCs]in an M-to-1 free-space optical[FSO]*** from UDCs’nonorthogonal nature,the sum throughput is *** first prove that the uniquelydecodable property still holds,even in ...
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This paper utilizes uniquely decodable codes[UDCs]in an M-to-1 free-space optical[FSO]*** from UDCs’nonorthogonal nature,the sum throughput is *** first prove that the uniquelydecodable property still holds,even in optical fading *** is further discovered that the receiver can extract each source’s data from superimposed symbols with only one processing *** to theoretical analysis and simulation results,the throughput gain is up to the normalized UDC’s sum rate in high signal-to-noise ratio *** equivalent desktop experiment is also implemented to show the feasibility of the UDC-FSO structure.
We consider the problem of designing binary antipodal code sequences (signatures) for overloaded code-division multiplexing (CDM) systems where the number of concurrent users/signals is greater than the code length. O...
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We consider the problem of designing binary antipodal code sequences (signatures) for overloaded code-division multiplexing (CDM) systems where the number of concurrent users/signals is greater than the code length. Our goal is to provide an overloaded code that can be constructed and decoded quickly and, more importantly, provide satisfactory recovery performance in conjunction with decoder design specifics. We first introduce a fast and practical method for constructing a code set by operating the Kronecker product with two smaller codes. Under such construction, a fast two-stage maximum-likelihood (ML) detection scheme can dramatically reduce the computational complexity of the ML decoder and make CDM systems practically implementable. To improve the performance in terms of bit error rate, we propose hierarchical criteria for code design, which aims at reducing the cross-correlation of code while maintaining a uniquelydecodable (errorless) code property. Simulation studies illustrate that the proposed code design can provide satisfactory performance with low-complexity two-stage ML detection.
The independence number of one-order graph associated with a linear code is formulated. The formulation is represented by the parameters of the generator matrix.
The independence number of one-order graph associated with a linear code is formulated. The formulation is represented by the parameters of the generator matrix.
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