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SCIENCE CHINA
Information Sciences
March 2023, Vol. 66 130302:1–130302:14
https://doi.org/10.1007/s11432-022-3692-5
c
Science China Press 2023 info.scichina.com link.springer.com
.REVIEW .
Special Topic: Spectrum, Coverage, and Enabling Technologies for Intelligent 6G
SpectrumChain: a disruptive dynamic
spectrum-sharing framework for 6G
Qihui WU1,2, Wei WANG1,2,3*, Zuguang LI1,2 , Bo ZHOU1,2 ,
Yang HUANG1,2 & Xianbin WANG4
1College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics,
Nanjing 211106, China;
2Key Laboratory of Dynamic Cognitive System of Electromagnetic Spectrum Space,
Ministry of Industry and Information Technology, Nanjing 211106, China;
3No. 8511 Research Institute of CASIC, Nanjing 210007, China;
4Department of Electrical and Computer Engineering, Western University, Ontario N6A 5B9, Canada
Received 30 September 2022/Revised 19 December 2022/Accepted 18 January 2023/Published online 14 February 2023
Abstract The sixth-generation (6G) wireless network will support ubiquitous connectivity and diversified
scenarios to satisfy the requirements of various emerging applications. Full spectrum is a key enabler for
6G to achieve the ambitious goal of a Tbps-scale data rate. In this paper, we first review the scenario and
potential spectrum plan for 6G and then focus on SpectrumChain, a blockchain-based dynamic spectrum-
sharing (DSS) framework for 6G. The unique characteristics of blockchain for DSS are presented along with
key technologies. Finally, the conclusion and future development trends are discussed.
Keywords dynamic spectrum sharing, blockchain, 6G
Citation Wu Q H, Wang W, Li Z G, et al. SpectrumChain: a disruptive dynamic spectrum-sharing framework
for 6G. Sci China Inf Sci, 2023, 66(3): 130302, https://doi.org/10.1007/s11432-022-3692-5
1 Introduction
With the commercialization of the fifth-generation (5G) wireless networks, research on the sixth-
generation (6G) wireless network has started in academia and industry, aiming to support ubiquitous
connectivity and the Internet of intelligence. It is anticipated that 6G will evolve toward full spectrum,
full coverage, and full applications, supporting immersive extended reality (XR), holographic communi-
cation, digital twins, etc. [1–3]. Therefore, 6G network services are expected to present new development
trends, such as digitization, intelligence, and personalization. To support such diversified services with
unique service requirements, evolutionary and revolutionary technologies in architecture and key enablers
will be adopted in 6G [4]. On the one hand, the 6G network will integrate different network segments
ranging from conventional terrestrial networks to aerial and spatial networks, forming a space-air-ground
(SAG) integrated networking framework. On the other hand, new enhanced air interfaces and emerging
techniques will be adopted in physical layers and network layers.
Compared with their 5G counterparts, 6G networks are expected to achieve extreme connectivity
performance with a Tbps-scale data rate, which requires hundreds of MHz to tens of GHz of spectrum
resources to cater to capacity-hungry applications [5, 6]. As shown in Figure 1, spectrum res ources from
the sub-6 GHz band to millimeter wave (mmWave), terahertz (THz), and visible light communications
(VLCs) are applied to provide enhanced connectivity in different network segments.
Although the SAG integration brings special strength in coverage, it confronts challenges in spectrum
resource management and service orchestration. The integration of satellites and aerial moving platforms
makes the network topology highly dynamic, and the interference pattern becomes more complex than
that of a single terrestrial network. As the terrestrial networks began to use high-frequency bands,
* Corresponding author (email: wei wang@nuaa.edu.cn)
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:2
THz, Laser
Ku, Ka
mmWave
mmWave
mmWave
mmWave,
sub-6G
Sub-6G
Sub-6G
Sub-6G
Small-BS
Smart gird Smart healthcare
mmWave, sub-6G
Ku, Ka, sub-6G
Desert
Mountain Sea
Figure 1 (Color online) 6G scenario and spectrum usage.
such as the C-band and Ka-band, spectrum overlapping was more likely to occur, resulting in severe
mutual interference that rarely existed before. To avoid interference, spectrum resources are usually
exclusively allocated to different mobile network operators (MNOs) and vertical industries. Such coarse
resource management, however, further exacerbates the supply/demand imbalance for spectrum resources.
Therefore, one critical bottleneck for 6G is to realize secure, efficient, and fine-grained spectrum resource
management.
As a distributed ledger technology, blockchain establishes a distributed peer-to-peer trusted net-
work with cryptography and a consensus mechanism, and thus secure spectrum sensing, spectrum re-
source auctioning/trading, and spectrum access and regulation can be conducted without a trusted third
party [7, 8]. Combining crowd sensing with blockchain technology, efficient and cost-effective spectrum
sensing can be realized using the capability of sporadic sensing devices, forming an accurate and large-
scale spectrum situation for further spectrum use. With the consensus mechanism, the spectrum rights
of each owner can be confirmed and stored in the block before transactions, and thus the revenues of
participants can be guaranteed. Particularly, the consensus process can be combined with a spectrum
allocation strategy to avoid unnecessary computing [9]. With a smart contract deployed on the chain,
spectrum trading/sharing transactions can be automatically executed with predefined rules, which greatly
facilitates efficiency and justice. Moreover, with blockchain, each step during spectrum sharing can be
permanently recorded, and thus any violations can be traced back with on-chain transaction records.
Thus, blockchain technology naturally facilitates dynamic spectrum sharing (DSS), and blockchain-based
DSS technology is also considered a key enabler for 6G [10–15].
To advance the 6G vision, unified planning and scheduling of spectrum resources should be promoted.
In this paper, we first review the scenario and potential spectrum usage for 6G and then focus on a
blockchain-based DSS framework and related key techniques. The remainder of this paper is organized
as follows. In Section 2, we present the spectrum vision and requirement for 6G and briefly review
the current DSS architecture. Then, in Section 3, we introduce blockchain-enabled DSS, including the
unique advantages of blockchain for DSS and a hierarchical SpectrumChain architecture. In Section 4,
blockchain-empowered key technologies for DSS are presented. Section 5 concludes this paper.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:3
2 6G spectrum requirement and vision
To realize the full experience of 6G, ultrahigh data rates up to Tbps are expected. According to [16], a
data rate of 1 Tbps could be achieved with 25 GHz bandwidth ideally, under the multiple input multiple
output (MIMO) rank-4 configuration with 1024 quadrature amplitude modulation, while the required
bandwidth may increase to 33.3 GHz assuming 25% overhead. In 5G, although sub-6G and mmWave
bands were initially explored, their maximum available bandwidths are rather limited [17] and thus far
from meeting the demands of 6G. Therefore, the development and use of new frequency bands toward
higher frequencies at the THz and visible light (VL) bands and facilitating DSS are essential solutions
for 6G. In this section, we elaborate on 6G spectrum vision from these three aspects and then discuss
DSS in detail.
2.1 6G spectrum vision
The ambitious vision in 6G brings a formidable challenge that is substantially greater than evolved
5G [18]. In terms of the spectrum, exploring new spectrum bands and reusing existing spectrum resources
are required to continuously serve billions of citizens and massive Internet of Things devices everywhere.
2.1.1 6G new spectrum
For 6G spectrum usage, several critical factors should be considered, such as coverage, throughput, and
quality of service (QoS). Here, we first summarize the properties of different frequency bands.
•Low band: Frequency band below 1 GHz. This band can provide broad area coverage and deep
indoor penetration because of its excellent propagation characteristics.
•Mid band: Frequency range from 1 to 24 GHz. This band can provide relatively large contiguous
bandwidth (up to hundreds of MHz) to balance coverage and capacity. However, the bandwidth remains
insufficient for supporting throughput-hungry environments in the 6G era.
•High band: Frequency range from 24 to 300 GHz. This band comprises the mmWave band (24–
92 GHz) and the sub-THz band (92–300 GHz). The mmWave band can provide high-capacity services
and has been used in 5G, whereas the sub-THz band remains under exploration for ultrahigh capacity
and ultralow latency services in 6G, such as hologram and XR.
•THz band: Frequency range from 100 to 10 THz. Although this band can provide ultra-large trans-
mission capacity, it suffers from severe attenuation during transmission in the atmosphere because of its
high-frequency characteristics and molecular absorption characteristics. Therefore, THz is mainly applied
to satellite communications and short-range ground communication, including microscale communication
scenarios.
•VL band: Frequency range from 380 to 750 THz. The optical wireless communication system
over the VL band can provide a centimeter-level precision positioning service and realize fine motion
capture. Note that, as VLC does not generate electromagnetic radiation and is not susceptible to ex-
ternal electromagnetic interference, it is thus suitable in certain scenarios sensitive to electromagnetic
interference [19].
In the early stage of 6G, a candidate spectrum has been intensively discussed in academia and industry.
Even without confirmed standards, 6G will inevitably use all of the above frequencies to support various
scenarios, including wide coverage with low or high capacity and low coverage with high capacity and
low latency.
2.1.2 Enhanced DSS
Although vast spectrum resources in low, mid, and high bands can be used for 6G, they are still insufficient
to meet all of the 6G capacity demands, particularly under wide coverage constraints. Meanwhile, network
traffic demands are not evenly distributed in many aspects because of the uneven spatial and temporal
traffic patterns, imbalance in uplink and downlink, user variances among different operators, etc. The
variant network traffic loads cause a strong imbalance in spectrum demands, where the static spectrum
management diagram alone cannot meet the dynamic spectrum requests of different operators considering
spatial and temporal variance. DSS on top of cognitive radio is in urgent demand to improve the spectrum
use and promote high levels of adaptivity of different operators under guaranteed QoS and priority.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:4
As predecessors, licensed shared access (LSA) [20] and citizens broadband radio service (CBRS) [21,22]
have been developed in Europe and the US, respectively. For LSA, incumbent license holders can share
their owned spectrum resources with secondary users (e.g., mobile operators) in a controlled way to
improve spectrum use in the 2.3 GHz band. In contrast, CBRS supports three-tier dynamic access with
a spectrum access system (SAS) in the 3.5 GHz band [23], where the top tier includes incumbents with
the highest protection, the second tier is the prioritized access license holders, who pay for the spectrum
usage rights of the incumbents when they are free of use, and the lowest tier is general authorized access,
which is free to use without any protection.
Note that LSA and CBRS rely on either a centralized database or centralized management authority,
which may become a bottleneck for large-scale applications and may also suffer severe malicious attacks.
In addition, the QoS of secondary users cannot be well guaranteed without comprehensive regulations,
and any spectrum violation may not be traced, which substantially impedes the practical implementation
of DSS. In the 6G era, enhanced DSS will be developed by the above driving force and promoted by
emerging technologies, such as integrated sensing and communication, artificial intelligence (AI), and
blockchain [14, 24, 25 ].
2.1.3 Spectrum regulation
Spectrum regulation will play a pivotal role before full DSS can be applied in the 6G era. As spectrum
security affects not only the communication itself but also the carried services, spectrum regulation is
always a key concern in front of DSS. At the moment, passive regulation is dominant with less active in-
tervention. With the employment of various spectrum resources in 6G, the regulation requirement will be
more stringent than ever before. On the one hand, the regulators need to evaluate the usage or occupancy
of a shared spectrum for further policy making. On the other hand, potential intended/unintended in-
terference or jamming should be identified to manage the spectrum order in an open and highly dynamic
environment. In this case, blockchain provides a complete solution for spectrum security regulation,
which has never been achieved before. Particularly, the spectrum-sharing transactions and transmission
parameters of each source can be recorded on the chain in a tamper-proof manner, and the off-chain
spectrum sensing data can be recorded on the chain for data integrity verification. Then, interference or
jamming forensics and arbitration can be achieved by coordinating on-chain transaction traceability and
off-chain signal identification, which has never been achieved without the assistance of blockchain.
2.2 DSS architecture
Considering the strong desire for DSS, in this subsection, we overview the system architecture and
workflow of existing DSS, including centralized and decentralized solutions.
2.2.1 Centralized DSS architecture
For the centralized solution, advanced management nodes (AMNs) are introduced to minimize the mutual
interference among operators, managing and allocating spectrum resources shared among operators in a
unified manner.
As shown in Figure 2, each operator has one operation administration and maintenance (OAM) server
and multiple base stations (BSs), where the OAM server is responsible for spectrum assignment and
management of the assigned BSs. During DSS, each BS first sends the spectrum demand request to its
OAM server, and then OAM determines the spectrum demand and submits the demands to the AMN
to obtain spectrum resources. The AMN makes spectrum allocation decisions and returns the results to
OAM servers, after which each BS can dynamically change the operating frequency under the control of
the OAM server.
For the centralized DSS architecture, spectrum resource management can be conducted at either the
operator level or the BS level, which are detailed as follows.
•Operator level: The AMN manages spectrum resources at the operator level and does not partic-
ipate in the spectrum allocation of BSs within each operator. The OAM server forecasts and aggregates
spectrum demand within each operator and sends it to the AMN. The AMN allocates spectrum re-
sources to each OAM server, where spectrum allocation among different operators is conducted by the
OAM server rather than the AMN.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:5
Advanced
management node
OAM OAM
InterfaceInterface InterfaceInterface
BSBS BS
BS
MNO A MNO B
Figure 2 (Color online) Centralized DSS architecture.
•BS level: In this case, the AMN manages the spectrum resource allocation of each BS under
its administration. Each BS forecasts and aggregates spectrum demand and related parameters and
sends this information to the OAM server. Then, the OAM server performs strategic filtering to obtain
accurate spectrum requirements and sends requests to the AMN. Finally, the AMN executes the spectrum
allocation decision of each BS.
2.2.2 Decentralized DSS architecture
In the centralized cross-operator spectrum-sharing architecture, operators cannot directly communicate
with each other but must collect and process transactions through a central AMN. As shown in Figure 3,
for the decentralized architecture, there is no AMN, and each MNO is configured with a spectrum
controller that is an independent physical entity or a functional module for spectrum-sharing decisions.
The spectrum controller is integrated into a physical entity, such as an OAM server, and can interact with
other spectrum controllers through predefined communication interfaces. With the interaction between
different spectrum controllers, multiple operators can exchange information and negotiate spectrum-
sharing rules. The corresponding DSS workflow is given as follows.
•Each BS reports spectrum requests to the spectrum controller, where the request information includes
the traffic load and service requirements.
•The spectrum controller calculates spectrum demand for each BS according to the collected infor-
mation.
•The spectrum controllers interact with each other to share the spectrum demand information (e.g.,
the available channel and power).
•The spectrum controller updates available spectrum resources based on the shared information from
other spectrum controllers.
•The spectrum controller allocates available channels to every BS.
•Each BS configures available channels to the associated users.
Note that even though centralized and distributed DSS have been proposed, they have not been well-
adopted in practice because of the lack of proper incentive mechanisms, QoS guarantees, and security and
privacy concerns. To facilitate flexible and efficient spectrum management, innovative new technologies
such as AI and blockchain are required in 6G.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:6
MNOMMNON
Spectrum sharing
Spectrum confirmation
Spectrum
controller M Spectrum
controller N
OAMMOAMN
MBSM
MBSNSBS1
SBS1
SBS2
SBS1
SBS2
MBS
Figure 3 (Color online) Decentralized DSS architecture.
3 Blockchain-enabled DSS for 6G
As an enabling technology with the important characteristics of decentralization, transparency, and trace-
ability, blockchain opens up new opportunities for DSS, and it is considered a promising solution and key
enabler for DSS in future 6G wireless networks [10–12, 26–28]. For example, with blockchain, a decen-
tralized DSS framework is constructed to facilitate trusted spectrum sharing between spectrum providers
and spectrum requestors without a third proxy, and the consensus mechanism provides a feasible way to
solve the channel contention problem where multiple users compete for unlicensed bands.
In this section, we first summarize the unique features and advantages that blockchain can bring for
DSS and then present a multilayer hierarchical blockchain-enabled DSS framework.
3.1 Unique advantages of blockchain for DSS
In this subsection, we elaborate on the specific potentials and benefits of blockchain for DSS that cannot
be achieved using conventional technology.
•Incentive mechanism: To motivate users or operators who have idle spectrum resources for DSS,
proper incentive rewards should be guaranteed. In conventional DSS systems, the reward for DSS is
usually handled by the central authority; thus, the revenue of the participants may not be ensured
because of the inequality between the two parties. With blockchain, the obligation and responsibility can
be clearly defined as an agreement in a smart contract, and thus the expected rewards can be ensured [29].
•Immutability: The unique data structure of blockchain makes it almost impossible to modify
previous data, which guarantees data integrity. In this way, blockchain can be integrated with the
spectrum monitoring and spectrum transaction system, where the sensing data (or data abstract) and
transaction details can be directly recorded in blockchain with a tamper-proof nature and traceability
and thus can provide proof-of-existence for spectrum regulation arbitration.
•Consensus: Consensus is the core for guaranteeing the consistency of the distributed blockchain
system, e.g., the proof-of-work (PoW) consensus in bitcoin relies on a complex mathematical problem,
costing much computing and energy resources. However, the spectrum resource allocation problem in
wireless communications is nonconvex in general and thus requires intensive computing resources to
obtain the optimal solution. This attribute naturally caters to the PoW mechanism. By combining PoW
and conventional spectrum allocation algorithms, the heavy meaningless of computation can be used
to calculate the spectrum allocation solutions, as in [30]. Moreover, the consensus mechanism can also
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:7
help the users to reach an agreement for spectrum access competition, such as the consensus-before-talk
mechanism [31], and dynamic spectrum access [32].
•Smart contract: A smart contract is a chaincode programmed with a certain logic and is auto-
matically executed once the predefined conditions are satisfied [33]. In this way, transactions can be
automatically implemented with a smart contract, which greatly improves efficiency.
•Security and privacy: During spectrum trading and auctioning, the identity of relevant users
may be revealed, which brings severe privacy concerns to participants. In addition, the spectrum usage
information may somehow disclose the behavior or patterns of relevant users; for example, the spectrum
sensing data may contain location information. By introducing blockchain, participants can anonymously
achieve secure transactions, which greatly promotes DSS in the 6G era.
Some studies have considered blockchain in DSS, such as [9,12, 22,34–38]. The authors of [34] divided
the SAS structure based on blockchain into two levels of chains for different service objects, i.e., a global
chain and a local chain. The global chain serves servers and regulators of cross-international businesses,
while the local chain serves users who use spectrum resources in local areas. The authors of [35] used
blockchain technology to design a secure and reliable trading platform for spectrum sharing between
primary users and secondary users, in which each user node anonymously uploads its own information
using ring signature technology. Because of its strong anonymity, ring signature technology has been
studied in many articles to design privacy protection mechanisms with high security. For example, the
authors in [9] used ring signature technology to prevent the personal data exposure of users participating
in DSS on the blockchain. The authors of [38] combined blockchain and auction theory to design a reverse
auction mechanism to support many wireless access requirements and dynamic user service requests under
the background of beyond 5G.
However, because of the massive spectrum users, ultra-large spectrum data, and very stringent de-
lay requirements in a time-varying environment, the popular public blockchain may not be suitable for
large-scale DSS. Compared with a public blockchain, a consortium blockchain has the merit of flexible
node control and management and caters to the efficiency and scalability requirements of large-scale
DSS1). Given these attributes, consortium blockchain will be the most suitable choice for DSS. In [39],
considering the different communication requirements in 5G networks, a consortium blockchain-based
spectrum planning framework was designed to improve spectrum efficiency. In Subsection 3.2, we fo-
cus on consortium blockchain and present a hierarchical DSS architecture for efficiency and scalability
requirements.
3.2 Blockchain-based hierarchical DSS framework
To enable secure large-scale spectrum sharing with guaranteed performance, such as up to thousands
of TPS efficiency, system scalability with different sharing granularity, and up to the second or less
confirmation delay, we propose a blockchain-based hierarchical DSS framework, i.e., SpectrumChain.
As shown in Figure 4, a hierarchical blockchain framework is developed, comprising one main chain
and multiple subchains. The main chain runs state/nation-level spectrum resource trading and regulation
publishing services, whereas each subchain runs local spectrum sharing. The main chain comprises
possibly multiple MNOs, a regulator, and multiple SAS servers, where MNOs can sell/buy spectrum
resources with each other for their own demand, and the regulator can publish regulative information for
security and fair spectrum sharing. A subchain is curated by a local committee comprising an SAS server
and multiple spectrum controllers, where spectrum controllers can rent spectrum resources to meet BSs’
spectrum demand. The SAS server may update the data of the subchain to the main chain at a certain
frequency. Compared with the existing SAS architecture, the hierarchical SpectrumChain architecture
can achieve a consensus-based fault-tolerant decision process at the global level (for regulation) and the
local level (for local spectrum sharing) [34]. This capability not only facilitates the DSS processing
efficiency but also guarantees certain isolation between different services with flexible scalability. We
elaborate on the functionalities of SpectrumChain as follows.
3.2.1 Main chain
The main chain is a consortium blockchain, including service provider nodes, a regulator node, and SAS
servers, and it mainly focuses on global-level spectrum sharing, spectrum regulation, and information
1) It is reported that up to several tens of thousands of transactions per second (TPS) of a single chain can b e achieved under
the consortium blockchain framework.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:8
Blockchain N
Main chain layer MNO Distributed ledger Regulator
Blockchain 2
Blockchain 1
Subchain layer
SAS server
SC SC
SC
SC
BS
Phone
PC
Physical layer
Smart city
Vehicle Vehicle
communication
UAV
Smart factory
CBSD
witness
Figure 4 (Color online) Hierarchical DSS framework.
synchronization. The main functionalities are described as follows.
•Spectrum sharing: Global-level spectrum sharing is realized on the main chain to achieve large-
scale coarse resource sharing among different services or vertical industries, which greatly facilitates the
development of various 6G scenarios.
•Regulation publication: To facilitate secure and efficient DSS on the chain, regulator nodes
integrate regulation policies into a smart contract, which is deployed as chaincodes on the blockchain.
The regulation rules may be updated regularly to facilitate dynamic management.
•Information synchronization: Each SAS server node on the main chain can synchronize the
data of the distributed spectrum ledger with the SAS server nodes on the subchain and delivers the rules
published on the main chain to each subchain.
The main chain is mainly responsible for global information synchronization and service level spectrum
resource sharing within a large area. Since the transaction throughput and frequency are not very large,
the throughput and delay performance requirements for the main chain are not very stringent.
3.2.2 Subchain
The subchain is designed for spectrum sharing within each local DSS zone. Participants on each subchain
comprise the SAS servers and spectrum controllers of MNOs. The user terminals of MNOs are connected
to the corresponding nearby BSs for wireless services, and the BSs monitor and analyze the spectrum usage
and spectrum demand within the region at a relatively small time scale, e.g., a several hours or days level.
Then, the BSs send the spectrum request to the corresponding spectrum controller. According to the
request information collected from the BSs, each spectrum controller can determine the spectrum demand
during a period and choose to act as a spectrum buyer or seller. The spectrum-sharing transactions among
spectrum controllers are recorded on the chain and synchronized to the main chain at a certain frequency.
The two types of transactions on the subchain are given as follows.
•Channel update transaction: A SAS server issues a channel update transaction, which means a
change in available channels when the server receives a regulation update from the main chain.
•Spectrum-sharing transaction: A spectrum controller issues spectrum-sharing requests in the
local spectrum zone. Each spectrum controller on the subchain can adaptively act as a spectrum provider
or spectrum requestor based on its demand.
Since the subchain controls DSS at a relatively fine-grained level compared with the main chain, the
requirements on transaction throughput and transaction or consensus delay for the blockchain system
performance will be much more stringent. Advanced lightweight architecture, efficient consensus, and
channel isolation techniques may be adopted at each subchain to improve performance.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:9
Executor
Task
response Task
allocation
Data
submission Receive
rewards
Blockchain network
Broadcast task
Publish sensing
task
Synchronize
ledger Package
transaction
Verify data
Receive data
Requester Blockchain node Blockchain node
Figure 5 (Color online) Blockchain-based crowd spectrum sensing mo del.
4 Blockchain-enabled technologies for DSS in 6G
In the previous section, we presented the SpectrumChain architecture to build an ideal framework for
future DSS. In this section, we further elaborate on several key enablers under this architecture and then
identify the particular advantages of blockchain for these technologies.
4.1 Blockchain-based crowd spectrum sensing
Crowd sensing is an emerging data aggregation paradigm with high mobility and scalability [40], and it can
greatly reduce the operation and maintenance costs of a sensing network [41]. Combining crowd sensing
and spectrum sensing can build efficient large-scale and high-precision spectrum data acquisition and
facilitate spectrum situational awareness. However, traditional crowd sensing is vulnerable to malicious
attacks because of its centralized architecture [42,43]. The process of sensing tasks will consume power,
computing, and storage resources, which need to be compensated for with reasonable rewards. Otherwise,
rational users may refuse to participate in crowd-sensing tasks [44]. More importantly, the spectrum
sensing data submitted by participants may contain their time and location information, through which
their behaviors can be inferred, and thus their private information is disclosed. Therefore, to facilitate
crowd sensing, a fully distributed, secure, and efficient platform with privacy-preserving and guaranteed
incentives for participants should be built.
Considering the unique properties of blockchain as described in the previous section and the require-
ments for crowd sensing, crowd sensing integrated with blockchain has become a fascinating solution for
spectrum sensing in future 6G systems. As shown in Figure 5, blockchain-based crowd sensing mainly
comprises a task requester, task executor, and blockchain network, whose roles are described as follows.
•Task requester: The requester represents the organization that has spectrum sensing tasks and
wants to acquire spectrum sensing data. The requester recruits possible task executors to work for them
by publishing sensing tasks and pays them according to the obtained sensing data.
•Task executor: Task executors are those who respond to the task request and can conduct sensing
tasks with their own devices. They execute sensing tasks and provide sensing data to obtain the reward
from the requester.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:10
•Blockchain network: The blockchain network is the basis of the system. The transactions be-
tween the requester and executor are recorded on the chain. By leveraging blockchain, no central server
is required; thus, the blockchain network can resist malicious attacks and improve stability and reliabil-
ity. Moreover, since the transaction is recorded on the blockchain in a tamper-proof manner, fraud or
falsification can be avoided.
The detailed procedure of blockchain-enabled crowd sensing is described as follows.
•Task publishing stage: The task requester first publishes sensing tasks by deploying a specific
smart contract on the blockchain, wherein the requester can set task requirements, rewards, etc. Then,
the blockchain node broadcasts the task in the network, and task executors can query the published tasks
on the blockchain.
•Task performing stage: Candidate task executors decide whether to participate in the task based
on the task information and their own capability. If the task can be completed, a candidate may send
a task response to the blockchain. Then, the pre-deployed smart contract will select candidates and
allocate tasks. Upon receiving the notification, the selected candidates become task executors to perform
the spectrum sensing tasks.
•Task-ending stage: Each task executor submits the collected sensing data to the blockchain node,
which will be verified by the blockchain nodes with certain algorithms. Then, the blockchain node will
package the transaction into a new block for consensus and update the ledger once an agreement is
reached. Finally, the task publisher will obtain the collected sensing data, and then the smart contract
will automatically distribute the reward to task executors.
On the basis of the above description, the unique advantages of blockchain for crowd sensing are
summarized as follows.
•Blockchain provides a secure and trusted platform without a centralized trusted authority, resulting
in improved system reliability and stability.
•The rewards for the participants can be guaranteed with blockchain and a smart contract. Thus,
cheating, such as free-riding and false reporting, can be avoided.
•The original sensing data or data abstract can be permanently recorded on the blockchain, and thus
data falsification can be prevented, which ensures the reliability of the sensing process.
•The private information of the participants can be well preserved with anonymous identity on the
chain. Therefore, more potential participants can be encouraged to participate in crowd sensing.
Regarding these advantages, some studies on blockchain-based crowd-sensing have appeared in the liter-
ature. In [45], the authors proposed a decentralized crowd-sourcing framework on the basis of blockchain,
named CrowdBC. They used a smart contract to perform crowd-sourcing tasks and verified the feasibility
of the proposed scheme through software prototypes and real datasets on Ethereum. The authors of [46]
illustrated a blockchain-enabled service architecture for the intelligent perception of SAG-integrated ve-
hicular crowd sensing and constructed a unified representation model. Then, they proposed a tensor
computing-based incentive mechanism to encourage vehicles to participate in completing tasks, ensure
the safety of the entire process, and maximize social welfare. A blockchain-based mobile crowd-sensing
system was developed to overcome the shortcomings of traditional MCS systems in [41]. It used miners
to verify sensing data, designed a dynamic reward ranking incentive mechanism, and developed a sensing
data quality detection scheme. The authors of [41] also built a prototype on Ethereum and conducted
extensive experiments in real factory studios.
4.2 Blockchain-enabled spectrum trading
At present, the spectrum allocation mode mainly includes an administrative examination and approval
approach and an auction-based marketing approach. An administrative approach is still the most typical
method for spectrum allocation but suffers from high administrative and maintenance costs. Conversely,
spectrum trading or auctioning may facilitate DSS efficiently [47]. In contrast to the centralized database-
based approach, the multi-party maintained and distributed ledgers of blockchain combined with cryp-
tography and a consensus mechanism can achieve secure and effective spectrum management without
a proxy [48]. With a smart contract, DSS can be automatically executed. Thus, blockchain-enabled
DSS has recently been intensively investigated. Kotobi et al. [49] introduced a virtual currency (i.e.,
spec-coins) to stimulate dynamic spectrum access, where the spec-coins can be used to pay for spectrum
access. A blockchain-based secure spectrum auction was considered in [50], which obtains idle frequency
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:11
Blockchain network
Memory pool 2. Collect spectrum requests
3. Make spectrum
sharing strategy
4. Upload
the strategy
7. Reply the result
Spectrum sharing
ledger
6. Update a block
5. Make a
consensus
decision
Consensus nodes
Primary node
1. Budget
7. Reply the
result
9. Licensed
spectrum
8. Pay
spectrum coins
Spectrum
requestor n
Spectrum
shortage
1. Bandwidth
7. Reply the
result Spectrum
provider m
Spectrum
enough
Figure 6 (Color online) Blockchain-enabled DSS workflow.
bands with spectrum monitoring to encourage authorized users to share a spectrum. The workflow of a
typical blockchain-based DSS is shown below.
Although blockchain provides a trusted platform for spectrum trading and auctioning, the correspond-
ing trading and auctioning algorithms should be designed to satisfy different objectives. As shown in
Figure 6, spectrum requestor msubmits the spectrum requesting message MSGreq with its digital sig-
nature to the memory pool through its local client, i.e., MSGreq ={idm,sigm, Qm,locm,depm,slotno},
where idmand sigmare the digital identity (ID) and signature of m, respectively. Qmand locmare its
total budget and location information, respectively. depmis its deposit for spectrum sharing, and slotno
is the slot number. On the spectrum provider side, spectrum provider nsends the spectrum providing
message MSGpro ={idn,sign,locn, Bn, Cn,depn,slotno}with its digital signature to the memory pool,
where Cnis the cost per unit bandwidth of n.
On the consortium blockchain, a primary node is selected to collect spectrum requesting and supplying
messages at the beginning of each slot. Next, it executes the DSS smart contract to obtain the spectrum-
sharing strategy, which is then submitted to consensus nodes as a proposal. Consensus nodes include
endorsers and orderers, which validate and sort the proposal, respectively. After that, the proposals are
packaged into a new block, and each node on the chain updates the ledger by adding the block. Spectrum
requestors pay the providers after obtaining the spectrum usage rights according to the trading results
in the ledger. If any participant violates the spectrum-sharing rule, the deposits will be confiscated.
Although the consortium blockchain has higher TPS performance than the public blockchain, further
improvements in performance in DSS scenarios with highly dynamic environments should be sought,
particularly the consensus delay performance.
4.3 Blockchain-enabled spectrum regulation
To fully reap the benefits of DSS in 6G, comprehensive and in-depth spectrum regulation is required by
evaluating the spectrum usage, managing the interference and jamming, and maintaining the security
operation. On the one hand, crowd sensing provides large-scale and high-precision spectrum sensing
capability so that the global spectrum security situation can be obtained. To provide dynamic spectrum
access decisions for different services, a spectrum resource pool should be constructed. The spectrum
situation also allows the spectrum usage of each MNO to be evaluated. On the other hand, spectrum
regulation guarantees normal operation and identifies illegal transmissions, such as black radio, malicious
jamming with high transmission power, and unintended signal transmission. However, the full spec-
trum applications in 6G and SAG integrated networking architecture make spectrum regulation a very
challenging issue.
By leveraging blockchain, complete transaction tracing, sensing deposit, signal identification, and dis-
pute arbitration solutions can be achieved with on-chain and off-chain coordination. A completely trace-
able full-process supervision mechanism can be established based on its tamper-proof characteristics,
including on-chain registration, spectrum trading, and spectrum regulation. As shown in Figure 7, the
regulation model comprises MNOs (including spectrum requestors and spectrum providers), a blockchain
network, and an off-chain monitoring system. The entire regulation procedure is described as follows.
Wu Q H, et al. Sci China Inf Sci March 2023 Vol. 66 130302:12
Spectrum sharing
Spectrum demander
Upload sharing
information
Upload BS’s
information
Upload BS’s
information
Spectrum provider
Upload monitoring
information
Query
information
Regulator
Figure 7 (Color online) Spectrum regulation model.
•The BSs belonging to each MNO register on the blockchain network to obtain their public/private
keys and certificates. The registration information includes the locations, antenna or radiation patterns,
predefined modulation type, and maximum transmission power. The registered information cannot be
falsified and can be traced by querying the distributed ledger. Meanwhile, the monitoring devices also
register their ID, locations, and operating parameters on the chain.
•Each MNO can adaptively act as a spectrum demander or provider and performs spectrum trading
or auctioning with other MNOs. The sharing transactions among MNOs are recorded on the chain.
•The monitoring devices continuously monitor the considered area at a predefined spectrum band
under the blockchain-enabled crow sensing framework. The original sensed data or data abstract is
recorded on the chain for data integrity verification.
•Each MNO can launch an interference complaint, including the interfering area, frequency, and time.
•The regulator receives the complaint and then traces the original sensing data with the parameters
in the complaint. With sensing data analysis, signal identification and localization algorithms can be used
to identify the position, modulation, and transmission power of the jamming signal. With the analyzed
information, the regulator also traces the on-chain transaction recordings for comparison to make an
adjudgement.
•The arbitration results are recorded on the chain for further processing.
5 Conclusion
In this paper, we provide an overview of the vision and requirements for 6G in terms of spectrum
usage. Then, we introduce a blockchain-enabled DSS framework by identifying the unique advantages
of blockchain for DSS. The hierarchical SpectrumChain DSS architecture with consortium blockchain is
presented in detail. Moreover, we also present blockchain-enabled technologies for 6G DSS, including
crowd spectrum sensing, spectrum trading, and spectrum regulation. However, applying blockchain for
6G DSS remains incipient, and more research efforts covering DSS-related techniques and the fundamental
blockchain revolutions should be required with global cooperation. We hope that this paper can provide
a fundamental basis and guidance for researchers to pursue more advanced solutions to soon realize 6G
DSS.
Acknowledgements This work was supported in part by National Key R&D Program of China (Grant No. 2020YFB1005900),
National Natural Science Foundation of China (Grant No. 62001220), Jiangsu Provincial Key Research and Development Program
(Grant No. BE2022068), Natural Science Foundation of Jiangsu Province (Grant No. BK20200440), Future Network Scientific
Research Fund Project (Grant No. FNSRFP-2021-YB-03), Young Elite Scientist Sponsorship Program, China Asso ciation for
Science and Technology, and Research Fund of Sony (China) Limited.
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