Transformation of a Rayleigh fading channel intoa set of parallel AWGNchannels and its advantage for coded transmission

Reinhardt, M.; Lindner, J.

doi:10.1049/el:19951468

Cited by 26 publications

(5 citation statements)

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“…The optimal spreading codes in asymmetric AWGN model is studied in [34] via the concept of Majorization and Schur-concavity [35] of the sum-capacity with respect to eigenvalues of HH H . While AWGN channel capacity depends on the spreading codes through their crosscorrelations [33], [34], the transmission of the signal over the i.i.d Rayleigh fading channel destroys the orthogonality of the spreading codes [36]. This, together with the hypotheses on the availability of only channel statistics, allow the spreading codes to be taken from the set of vectors {w k } with positive values and independent of the small-scale fading gains, as stated in the following proposition, Proposition 1.…”

Section: Ergodic Capacity Of the Channelmentioning

confidence: 99%

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Asgharimoghaddam

Kaleva²,

Tölli

2021

IEEE Trans. Commun.

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Low-density spreading non-orthogonal multiple-access (LDS-NOMA) is considered where K singleantenna user-equipments (UEs) communicate with a base-station (BS) over F fading sub-carriers.Each UE k spreads its data symbols over d k < F sub-carriers. We aim to identify the LDS-code allocations that maximize the ergodic mutual information (EMI). The BS assigns resources solely based on pathlosses. Conducting analysis in the regime where F , K, and d k , ∀k converge to +∞ at the same rate, we present EMI as a deterministic equivalent plus a residual term. The deterministic equivalent is a function of pathlosses and spreading codes, and the small residual term scales asWe formulate an optimization problem to get the set of all spreading codes, irrespective of sparsity constraints, which maximize the deterministic EMI. This yields a simple resource allocation rule that facilitates the construction of desired LDS-codes via an efficient partitioning algorithm. The acquired LDS-codes additionally harness the small incremental gain inherent in the residual term, and thus, attain near-optimal values of EMI in the finite regime. While regular LDS-NOMA is found to be asymptotically optimal in symmetric models, an irregular spreading arises in generic asymmetric cases. The spectral efficiency enhancement relative to regular and random spreading is validated numerically.

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Section: Ergodic Capacity Of the Channelmentioning

confidence: 99%

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Asgharimoghaddam

Kaleva²,

Tölli

2021

IEEE Trans. Commun.

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“…The corresponding conventional problem without sparsity constraints is considered in [17], [18] for additive white Gaussian noise (AWGN) channel. While AWGN channel capacity depends on the spreading codes through their cross-correlations, the transmission of the signal over a Rayleigh fading channel destroys the orthogonality of the spreading codes [19]. This together with the assumption of obtaining the spreading codes based on pathlosses limit the search space to the set of vectors w k ∈ R + with positive values, and independent of the smallscale fading gains.…”

Section: A Ergodic Capacity Of the Channelmentioning

confidence: 99%

Resource Allocation in Low Density Spreading Uplink NOMA via Asymptotic Analysis

Asgharimoghaddam

Tölli

2020

2020 IEEE International Symposium on Information Theory (ISIT)

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Low density spreading non-orthogonal multipleaccess (LDS-NOMA) is considered where K single-antenna user equipments (UEs) communicate with a base station (BS) over F fading sub-carriers. Each UE k spreads its data symbol over d k < F sub-carriers. Given d k , ∀k as design parameters, we characterize the resource allocation solutions that closely maximize the ergodic mutual information (EMI) in a scenario where the BS assigns resources solely based on the UEs' pathlosses. Conducting analysis in asymptotic limit where F , K, and d k , ∀k converge to +∞ at the same rate, we present EMI in terms of a deterministic equivalent plus a residual term. The deterministic equivalent is given in terms of pathloss values and LDS-codes, and the small residual term scales as O( 1d 2 ) where d = min{d k , ∀k}. We formulate an optimization problem to get the setC * of all spreading codes, irrespective of sparsity constraints, which maximize the deterministic equivalent of EMI. The spreading codes inC * with desired sparsity are obtained via a simple and efficient algorithmic solution. In the finite regime, the residual term is shown to be a small incremental gain for the sparse solutions inC * , which is dictated mainly by d k , ∀k values. Accordingly, we show that the solutions inC * with desired sparsity yield close to optimum values of EMI in the finite regime. Numerical simulation validates the attainable spectral efficiency enhancement as compared to regular, and random spreading.

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“…The optimal spreading codes in asymmetric AWGN model is studied in [25] via the concept of Majorization and Schurconcavity [26] of the sum-capacity with respect to eigenvalues of HH H . While AWGN channel capacity depends on the spreading codes through their cross-correlations, the transmission of the signal over a Rayleigh fading channel destroys the orthogonality of the spreading codes [27].…”

Section: Ergodic Capacity Of the Channelmentioning

confidence: 99%

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Asgharimoghaddam¹,

Kaleva²,

Tölli³

2019

Preprint

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Low density spreading multiple-access is considered where K single-antenna user equipments (UEs) communicate with a base station (BS) over F sub-carriers. Each UE k spreads its data symbol over d k < F sub-carriers, while d k = 1 corresponds to a power domain non-orthogonal multiple-access (NOMA). For given design parameters d k , we provide an analytical framework for characterizing resource allocations that closely maximize the ergodic sum-rate in the considered NOMA schemes.In particular, we are interested in a scenario where the BS assigns resources solely based on the UEs pathloss values. To this end, we let F , K, and d k to grow into mF , mK, and md k , respectively, such that the overlap of UEs on sub-carriers remain intact. In asymptotic regime where m → ∞, we derive a deterministic expression for the ergodic sum-rate in terms of pathloss values and spreading codes. This is incorporated into an optimization problem to characterize the set of all asymptotically optimal spreading codes irrespective of sparsity constraints. Then, algorithmic solutions are proposed to find the asymptotic codes with desired number of non-zero elements in each of the spreading codes, and the number of UEs transmitting on each sub-carrier. We show that the attained codes get the maximum of ergodic sum-rate in finite regime up to a small gap. Numerical simulation validates the attainable spectral efficiency enhancement as compared to the random assignment of spreading codes. I. INTRODUCTION Consider a scenario where K single-antenna user equipments (UEs) communicate with a base station (BS) over F sub-carriers. Given an overloaded setting with K > F , inevitable multiple access interference (MAI) occurs that needs to be dealt via non-orthogonal multiple access (NOMA) techniques. In order to distinguish UEs at the BS, one can add redundancy by spreading UEs symbol over d k sub-carriers. The NOMA scenario where d k values are much smaller than F is dubbed as multi-carrier low density spreading multiple access (MC-LDSMA) in H. Asgharimoghaddam and A. Tölli are with the Centre for Wireless Communications

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Transformation of a Rayleigh fading channel intoa set of parallel AWGNchannels and its advantage for coded transmission

Cited by 26 publications

References 1 publication

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Resource Allocation in Low Density Spreading Uplink NOMA via Asymptotic Analysis

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

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