ZTE Communications ›› 2021, Vol. 19 ›› Issue (4): 3-15.DOI: 10.12142/ZTECOM.202104002
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ZHANG Zhengquan1,2(), LIU Heng1, WANG Qianli1, FAN Pingzhi1
Received:
2021-10-18
Online:
2021-12-25
Published:
2022-01-04
About author:
ZHANG Zhengquan (Supported by:
ZHANG Zhengquan, LIU Heng, WANG Qianli, FAN Pingzhi. A Survey on Low Complexity Detectors for OTFS Systems[J]. ZTE Communications, 2021, 19(4): 3-15.
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URL: https://zte.magtechjournal.com/EN/10.12142/ZTECOM.202104002
Figure 2 OTFS detector structures: (a) DD-domain non-iterative OTFS detector; (b) DD-domain iterative OTFS detector; (c) non-iterative joint TF- and DD-domain OTFS detector; (d) joint non-iterative TF-domain and iterative DD-domain OTFS detector; (e) iterative joint time- and DD-domain OTFS detector; (f) iterative joint TF- and DD-main OTFS detector; (g) iterative joint time-, TF- and DD-main OTFS detector; (h) learning-enabled OTFS detector
Figure 3 OTFS detector classifications: (a) non-iterative and iterative OTFS detectors; (b) single domain and multi-domain OTFS detectors; (c) conventional and learning-based OTFS detectors
Ref. | Detector Structure | Detector Structure Type | Domain | Basic Idea | Advantage | Disadvantage |
---|---|---|---|---|---|---|
Refs. [ | Single- domain OTFS detector | DD-domain non-iterative OTFS detection | DD domain | Adopting non-iterative detection algorithms (e.g., MMSE/ZF) in DD domain | Signal detection is only performed in DD domain; Non-iterative signal detection algorithms are relatively low complexity. | Non-iterative signal detection algorithms suffer from some performance loss. |
Refs. [ | DD-domain iterative OTFS detection | DD domain | Adopting iterative detection algorithms, like MP/AMP and MRC etc., in DD domain | Iterative detection algorithms can achieve better performance. | Iterative detection will increase the complexity of algorithm design; the convergence of algorithms should be analyzed and ensured. | |
Ref. [ | Joint multi- domain OTFS detector | Non-iterative joint TF- and DD-domain OTFS detection | TF domain and DD domain | Joint TF- and DD- domain processing with non-iterative detection algorithms | Joint multi-dimension processing can achieve better detection performance; Joint multi-dimension processing can relax the processing requirements in DD domain. | Joint multi-dimension processing increases the complexity of designing OTFS detector. |
Refs. [ | Joint non-iterative TF-domain and iterative DD-domain OTFS detection | TF domain and DD domain | Employing TF MMSE equalizer to provide good initials for DD-domain iterative MRC detector | Introducing non-iterative TF MMSE equalizer can accelerate the convergence of DD-domain iterative MRC detector; iterative MRC detector can fully merge separable taps to obtain better performance. | TF detection is needed to provide initial estimates; iteration processing increases the complexity; need to add null symbols to construct full channel matrix. | |
Ref. [ | Iterative joint time- and DD-domain OTFS detection | Time domain and DD domain | Joint processing of time and DD domains to form a large iterative detection loop. | Iterative joint time- and DD-domain detection can achieve better performance and faster convergence by fully utilizing time- and DD-domain information. | Iterative joint time- and DD-domain detection increases the complexity of designing OTFS detector; a large amount external information exchange is inevitable. | |
Iterative joint TF- and DD-main OTFS detection | TF domain and DD domain | Joint TF and DD domains that form a large iterative detection loop. | Iterative joint TF- and DD-domain detection can achieve better performance and faster convergence by fully utilizing TF- and DD-domain information. | Iterative joint TF- and DD-domain detection increases the complexity of designing OTFS detector; a large amount external information exchange is inevitable. | ||
Refs. [ | Learning-based OTFS detection | DD domain | Using machine learning techniques to perform signal detection in DD domain or estimate some parameters in conventional OTFS detector. | It is relatively simple to design learning-based signal detection as a black box without understanding expert knowledge of OTFS detection; better detection performance is achieved. | Learning-based detection is un-explainable; more computing capability is required; massive training and testing datasets are necessary. |
Table 1 Summary of OTFS detector structures
Ref. | Detector Structure | Detector Structure Type | Domain | Basic Idea | Advantage | Disadvantage |
---|---|---|---|---|---|---|
Refs. [ | Single- domain OTFS detector | DD-domain non-iterative OTFS detection | DD domain | Adopting non-iterative detection algorithms (e.g., MMSE/ZF) in DD domain | Signal detection is only performed in DD domain; Non-iterative signal detection algorithms are relatively low complexity. | Non-iterative signal detection algorithms suffer from some performance loss. |
Refs. [ | DD-domain iterative OTFS detection | DD domain | Adopting iterative detection algorithms, like MP/AMP and MRC etc., in DD domain | Iterative detection algorithms can achieve better performance. | Iterative detection will increase the complexity of algorithm design; the convergence of algorithms should be analyzed and ensured. | |
Ref. [ | Joint multi- domain OTFS detector | Non-iterative joint TF- and DD-domain OTFS detection | TF domain and DD domain | Joint TF- and DD- domain processing with non-iterative detection algorithms | Joint multi-dimension processing can achieve better detection performance; Joint multi-dimension processing can relax the processing requirements in DD domain. | Joint multi-dimension processing increases the complexity of designing OTFS detector. |
Refs. [ | Joint non-iterative TF-domain and iterative DD-domain OTFS detection | TF domain and DD domain | Employing TF MMSE equalizer to provide good initials for DD-domain iterative MRC detector | Introducing non-iterative TF MMSE equalizer can accelerate the convergence of DD-domain iterative MRC detector; iterative MRC detector can fully merge separable taps to obtain better performance. | TF detection is needed to provide initial estimates; iteration processing increases the complexity; need to add null symbols to construct full channel matrix. | |
Ref. [ | Iterative joint time- and DD-domain OTFS detection | Time domain and DD domain | Joint processing of time and DD domains to form a large iterative detection loop. | Iterative joint time- and DD-domain detection can achieve better performance and faster convergence by fully utilizing time- and DD-domain information. | Iterative joint time- and DD-domain detection increases the complexity of designing OTFS detector; a large amount external information exchange is inevitable. | |
Iterative joint TF- and DD-main OTFS detection | TF domain and DD domain | Joint TF and DD domains that form a large iterative detection loop. | Iterative joint TF- and DD-domain detection can achieve better performance and faster convergence by fully utilizing TF- and DD-domain information. | Iterative joint TF- and DD-domain detection increases the complexity of designing OTFS detector; a large amount external information exchange is inevitable. | ||
Refs. [ | Learning-based OTFS detection | DD domain | Using machine learning techniques to perform signal detection in DD domain or estimate some parameters in conventional OTFS detector. | It is relatively simple to design learning-based signal detection as a black box without understanding expert knowledge of OTFS detection; better detection performance is achieved. | Learning-based detection is un-explainable; more computing capability is required; massive training and testing datasets are necessary. |
Reference | Detection Algorithm | Algorithm Characteristic | Computational Complexity | Performance |
---|---|---|---|---|
Ref. [ | Classical MMSE | Non-iterative | UAMP>EP>AEP >MRC-rake >VB >MP >Classical MMSE ≥low complexity MMSE | |
Ref. [ | Low complexity MMSE | Non-iterative | ||
Ref. [ | lower-upper factorization -based MMSE | Non-iterative | ||
Refs. [ | MP | Iterative | ||
Ref. [ | MF-MP-PC | Iterative | ||
Ref. [ | GAMP | Iterative | ||
Ref. [ | UAMP | Iterative | ||
Ref. [ | ICMP | Iterative | ||
Refs. [ | MRC-rake | Iterative | ||
Ref. [ | EP | Iterative | ||
AEP | Iterative | |||
Ref. [ | VB | Iterative |
Table 2 Summary of computational complexity and performance
Reference | Detection Algorithm | Algorithm Characteristic | Computational Complexity | Performance |
---|---|---|---|---|
Ref. [ | Classical MMSE | Non-iterative | UAMP>EP>AEP >MRC-rake >VB >MP >Classical MMSE ≥low complexity MMSE | |
Ref. [ | Low complexity MMSE | Non-iterative | ||
Ref. [ | lower-upper factorization -based MMSE | Non-iterative | ||
Refs. [ | MP | Iterative | ||
Ref. [ | MF-MP-PC | Iterative | ||
Ref. [ | GAMP | Iterative | ||
Ref. [ | UAMP | Iterative | ||
Ref. [ | ICMP | Iterative | ||
Refs. [ | MRC-rake | Iterative | ||
Ref. [ | EP | Iterative | ||
AEP | Iterative | |||
Ref. [ | VB | Iterative |
Figure 9 Multiple access schemes for downlink hybrid OFDM-OTFS systems in multi-user scenario: (a) hybrid orthogonal frequency division multiple access (OFDMA) and orthogonal time frequency space multiple access (OTFSMA) in both DD and TF domains; (b) hybrid OFDMA and OTFSMA with overlap in the TF domain
Figure 10 BLER performance: (a) two-user orthogonal time frequency space (OTFS) systems without inter-user interference (IUI); (b) two-user hybrid OTFS-orthogonal frequency division multiplexing (OFDM) systems
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