TFH-MAC：一种分布式优先级多址接入方案

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"这篇研究论文提出了一种名为TFH-MAC(时频跳变多址接入控制)的分布式优先级多址访问方案，用于时频跳变通信的Ad Hoc网络，旨在解决分布式资源协调、避免冲突以及实现服务差异化的问题。通过引入信道占用率(COR)来指示时间频率资源块中的传输状态，并根据不同的交通类别分配预设的COR阈值和竞争窗口大小，以实现不同优先级的通信服务。" 在无线Ad Hoc网络中，节点之间直接通信，网络结构动态且自组织。时频跳变(TFH)通信是一种提高安全性和抗干扰能力的技术，通过在伪随机的时间槽和载波频率上发送数据。然而，这种技术在Ad Hoc网络中的应用面临着如何在分布式环境中有效地协调各个站点，共享时间/频率资源，防止碰撞，以及提供差异化的服务质量的挑战。 TFH-MAC协议是针对这些挑战设计的解决方案。该协议的核心在于引入了信道占用率(COR)的概念，这是一个反映网络中各节点在时间频率资源矩阵中占用情况的指标。通过分析和管理这个指标，协议能够监控网络资源的使用情况，避免过度拥堵，减少潜在的碰撞。为了实现服务差异化，TFH-MAC协议将流量分为不同的类别，并为每个类别分配不同的预设COR阈值和竞争窗口大小。高优先级的流量类别的COR阈值较低，这意味着它们有更高的概率获得信道使用权，而低优先级的流量则需要更大的竞争窗口，从而降低了它们的访问频率。这种策略确保了关键或紧急数据的高效传输，同时维持了网络的整体性能和稳定性。此外，TFH-MAC协议还可能包含冲突检测和解决机制，以及动态调整机制，以适应网络条件的变化。冲突检测允许节点在检测到碰撞后重新传输数据，而动态调整则可以基于网络负载和性能指标实时改变资源分配策略。 TFH-MAC协议通过引入创新的资源管理和优先级机制，为时频跳变通信的Ad Hoc网络提供了高效且公平的访问控制，提高了网络的整体效率和服务质量。这项工作对于理解Ad Hoc网络中的分布式通信策略以及优化无线资源管理具有重要的理论和实践意义。

A Distributed Prioritized Multiple Access Scheme

for Ad Hoc Networks Using Time-Frequency

Hopping Communications

Ruonan Zhang

,MiaoLi

,LinCai

,andBinLi

Northwestern Polytechnical University, Xi’an, Shaanxi, China

University of Victoria, Victoria, British Columbia, Canada

Abstract—In the time-frequency h opping (TFH) communica-

tions, a terminal transmits data at pseudo-random time slots

and carrier frequencies, leading to high security against eaves-

dropping and anti-interference capability. However, in an ad

hoc network using the TFH communications, it is challeng-

ing to coordinate stations in a distributed manner to share

the time/frequency resources, avoid collision, and provide ser-

vice differentiation. In this paper, we propose a distributed,

prioritized multiple access control (MAC) protocol for TFH-

based ad hoc networks, named TFH-MAC. In this scheme, the

channel occupancy ratio (COR) is introduced to indicate the

transmission of stations in a matrix of time-frequency resource

blocks. By assigning different predetermined COR thresholds and

contention window sizes to trafﬁc classes, the priorities in channel

access can be provided. Furthermore, the low-complexity random

linear coding (RLC) is employed to repair frames from time-

frequency spread segments with partial collision. In particular,

the segments correctly received in previous transmissions can

be combined with newly successfully received segments for

decoding. Thus, the transmission efﬁciency is increased. An

analytical model using mean value analysis is proposed to study

the performance of saturated TFH-MAC theoretically, and the

transmission probability, collision probability, throughout, and

frame service time are derived. Extensive simulation results have

veriﬁed the analytical model and demonstrated the optimal trafﬁc

load and resource matrix dimension to maximize the network

throughput.

Index Terms: time-frequency hopping communications; media

access control; service differentiation; mean value analysis; ad

hoc networks

I. INTRODUCTION

The time-frequency hopping (TFH) technique has been

widely used in complicated environments such as military

communications [1]. In the TFH communications, terminals

are assigned pseudo-random (PN) time and frequency-hopping

sequences, resulting in good anti-interference ability and com-

munication concealment against eavesdropping. Meanwhile,

a time-frequency hopping pattern can be regarded as a sub-

channel. Th e spreading also creates multiple sub-ch annels in

the joint time-frequency domain and several transmissions can

take place with limited in ter-user interference. If the stream

through a TFH sub-channel has overlap with those in other

subchannels, the information in each individual stream may

be recovered using error correction coding. Hence, the TFH

communications can allow mu ltiple simultaneou s streams and

exploit the multiplexing gain.

However, there are several critical issues to be addressed

while designing wireless a d hoc network based on TFH and

multi-channel (MC) communications. First, the time-frequency

hopping sequences are randomly assigned or generated, the

full orthogonality among spreading patterns is not guaranteed.

A multiple access mechanism should be combined with the

hopping patterns to schedule the transmission/retransmission

of frames and resolve collisions. Second, trafﬁc ﬂows can

be differentiated and p riorities in channel access for different

trafﬁc classes should be provided. Urgent messages and real-

time streams that need to be delivered before hard deadlines

should have higher priority in utilizing the time-frequency

channel resources. On the other hand, the delay-tolerant data

trafﬁc can be served only when there are sufﬁcient idle

channel resources. Third, the TFH pattern generation and

channel access coordination should be performed in a fully

distributed manner. Compared to the centralized mechanisms,

independent TFH and contention-based channel access have

favorable characteristics, such as dynamic self-organization,

easy maintenance, and high scalability.

Inspired by the attractive features and potential beneﬁt of

MC networking, the MC media access control (MC MAC) has

been investigated extensively in recently years. The authors

in [2] proposed a dynamic switching protocol which provided

two interfaces. One interface followed fast hopping and was

primarily for transmission, while the oth er performed slow

hopping and was generally for reception. Wireless nodes

could dynamically switch among channels and did not need a

dedicated control channel for congestion avoidance. For time

division multiple access (TDMA)-based MC MAC, a dynamic

time slot assignment protocol with FH, named unifying slot

assignment protocol (UASP), was proposed in [1]. It was

desinged to ensure the inter-node time synchronization and

adaptation to a self-organized network using FH. In [3], a

new TDMA MAC protocol was proposed for diverse trafﬁc in

hierarchical wireless sensor networks. The quality-of-service

(QoS) provisioning like loss and delay performance was

improved. The authors in [4] designed hopping sequences by

combining multiple difference sets, and proposed a difference-

set-based MC MAC to achieve high system throughput and

low delay by applying the hopping sequences to all users. The

communication channel recommendation MAC (CCR-MAC)

could recommend a better channel according to the channel

usage and topology information [5]. An analytical framework

for the MC cooperative MAC was proposed in [6], which

used two discrete-time Markov chains to separately model

2016 International Conference on Networking and Network Applications

DOI 10.1109/NaNA.2016.88

2016 International Conference on Networking and Network Applications

DOI 10.1109/NaNA.2016.88

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