Time and Frequency Synchronization for OTFS

Bayat, Mohsen; Farhang, Arman

doi:10.36227/techrxiv.19638375

“…. , D T p,N −1 ] T } realizes the 2D circular convolution in (10), with the L × L circulant matrices D p,n whose first columns are the n th column of D p , h DD = vec{H DD }, and v p = vec{V p }. Hence, from (11), h DD can be estimated using the LS or MMSE criterion, as…”

Section: Proposed Channel Estimation Techniquementioning

confidence: 99%

“…From (10), one may realize that 2D circular convolution can be implemented by multiplication in the frequency-time (FT) domain. Consequently, the received FT domain pilot signal can be represented as…”

Section: Low Complexity Implementation and Detection Considerationsmentioning

confidence: 99%

“…N are the FT domain counterparts of the corresponding DD domain signals in (10). It is worth noting that Z FT p can be directly calculated as Z FT p = F L Y p where the L × N matrix Y p includes the DT domain received pilot after removing its CP.…”

Section: Low Complexity Implementation and Detection Considerationsmentioning

confidence: 99%

“…In [3], a threshold-based channel estimation method was proposed. This method utilizes an embedded impulse pilot along with data that has a large power and is widely used for channel estimation and synchronisation in OTFS literature, [7]- [10]. More recently, in [11], a spline interpolation step in addition to the threshold-based estimation of [3] was proposed to improve the channel estimation accuracy.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Practical Pilot for Channel Estimation of OTFS

S.¹,

Farhang²

2022

Preprint

0

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The widely used embedded impulse pilot for channel estimation of orthogonal time frequency space modulation (OTFS) has a prohibitively large peak to average power ratio (PAPR). Hence, in this paper, we propose a novel embedded pilot with cyclic prefix (PCP) that has a significantly reduced PAPR compared to the impulse pilot. This is achieved by spreading the pilot power along the delay dimension using a constant amplitude Zadoff-Chu (ZC) sequence with a cyclic prefix (CP). We analytically derive upper bound PAPR expressions for the impulse pilot and the proposed PCP. Together with our numerical results, these upper bounds attest the significant PAPR improvement that is achieved by PCP. We also develop a twostage channel estimation technique with a superior performance to the threshold-based channel estimation for the impulse pilot. At the first stage, the channel is estimated by a linear estimator under the assumption of the channel being locally linear time invariant over each time-slot within the OTFS block. Taking advantage of the benefits that are offered by the CP in our proposed pilot structure, we develop a low complexity least squares based estimator for implementation of the first stage. At the second stage, we use the channel estimate from the first stage and the generalized complex exponential basis expansion model (GCE-BEM) to accurately estimate the full channel. Finally, we numerically anayze and show the superior estimation performance of our proposed channel estimator for PCP to the threshold-based estimator for the impulse pilot.

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“…In [3], a threshold-based channel estimation method was proposed. This method utilizes an embedded impulse pilot along with data that has a large power and is widely used for channel estimation and synchronisation in OTFS literature, [7]- [10]. More recently, in [11], a spline interpolation step in addition to the threshold-based estimation of [3] was proposed to improve the channel estimation accuracy.…”

Section: Introductionmentioning

confidence: 99%

A Practical Pilot for Channel Estimation of OTFS

S.¹,

Farhang²

2022

Preprint

0

View full text Add to dashboard Cite

The widely used embedded impulse pilot for channel estimation of orthogonal time frequency space modulation (OTFS) has a prohibitively large peak to average power ratio (PAPR). Hence, in this paper, we propose a novel embedded pilot with cyclic prefix (PCP) that has a significantly reduced PAPR compared to the impulse pilot. This is achieved by spreading the pilot power along the delay dimension using a constant amplitude Zadoff-Chu (ZC) sequence with a cyclic prefix (CP). We analytically derive upper bound PAPR expressions for the impulse pilot and the proposed PCP. Together with our numerical results, these upper bounds attest the significant PAPR improvement that is achieved by PCP. We also develop a twostage channel estimation technique with a superior performance to the threshold-based channel estimation for the impulse pilot. At the first stage, the channel is estimated by a linear estimator under the assumption of the channel being locally linear time invariant over each time-slot within the OTFS block. Taking advantage of the benefits that are offered by the CP in our proposed pilot structure, we develop a low complexity least squares based estimator for implementation of the first stage. At the second stage, we use the channel estimate from the first stage and the generalized complex exponential basis expansion model (GCE-BEM) to accurately estimate the full channel. Finally, we numerically anayze and show the superior estimation performance of our proposed channel estimator for PCP to the threshold-based estimator for the impulse pilot.

show abstract

Precise Positioning: When OTFS Meets Distributed Cooperative Positioning

emadi¹,

Hu²,

Wang³

2023

Preprint

0

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Precision positioning plays critical roles in 5G-Advanced and 6G systems for various indoor and outdoor applications. Conventionally, positioning accuracy can be dramatically degraded under non-line-of-sight channels or with moving terminal nodes (TNs). To overcome this issue, we propose an orthogonal time-frequency space (OTFS) based positioning with applying distributed cooperative positioning (DCoP) at the ends of TNs, which can yield an ultra-most precise positioning. This is so, since the positioning with OTFS is robust against channel delays and Doppler spreads, and superior to conventional orthogonal frequency-division multiplexing (OFDM) based positioning. Further, DCoP uses cooperations such that TNs can serve as additional anchor nodes (ANs) to others, and improves the positioning accuracy for all. With this proposal, we further elaborate the positioning-reference-signal with OTFS (PRS-OTFS) in delay-Doppler (DD) domain, and design an OTFS-transceiver that is backward compatible to OFDM. Furthermore, we also propose a DD-domain time-of-arrival estimation algorithm that exploits the OTFS waveform and outperforms conventional time-frequency based estimators. Moreover, we propose a loopy belief-propagation algorithm associated with belief-discretizing for an effective implementation and message exchange in DCoP. In addition, we show that the average Cramer-Rao low-bound per TN can decrease faster than linearly in the number of cooperating TNs. We illustrate with simulations that the proposed OTFS-DCoP scheme is very effective in improving positioning accuracy within a few iterations, and robust against double-selective channels.

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Time and Frequency Synchronization for OTFS

Cited by 5 publications

References 25 publications

A Practical Pilot for Channel Estimation of OTFS

A Practical Pilot for Channel Estimation of OTFS

A Practical Pilot for Channel Estimation of OTFS

Precise Positioning: When OTFS Meets Distributed Cooperative Positioning

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