DCSK-ARQ/CARQ系统：多径衰落信道上的性能优化与比较

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本文主要探讨了多径衰落信道上的一种创新性的通信系统设计——DCSK-ARQ/CARQ系统。DCSK，即差分混沌移位键控，是一种基于混沌理论的调制方式，因其抗衰落特性在低功耗和低成本无线通信领域备受关注。在这个研究中，作者提出了一种结合了差分混沌调制与自动重传请求（ARQ）和协作自动重传请求（CARQ）技术的系统，旨在提升系统的可靠性和效率。 ARQ是一种在数据传输过程中，如果接收到的数据包存在错误，发送方会重新发送的机制。而CARQ则在此基础上进一步增强了协作性，多个节点可以协同工作，通过共享错误检测信息，提高整体纠错能力。DCSK-ARQ/CARQ系统的设计目标是利用这些先进技术来对抗多径衰落带来的信号失真，从而改善通信质量。论文的主体部分详细分析了DCSK-ARQ/CARQ系统在中道多径Nakagami fading通道上的性能。Nakagami fading是一种常用的信道模型，用于模拟实际无线环境中的衰落效应。通过理论分析和数值仿真，研究结果显示DCSK-ARQ/CARQ系统在错误率和吞吐量方面显著优于传统的DCSK非合作（DCSK-NC）和协作（DCSK-CC）通信系统。此外，作者还深入研究了关键参数，如混沌序列的生成、编码效率、ARQ循环次数以及协作节点的数量等，对系统性能的影响。这些参数的优化对于实际无线应用场景具有重要意义，能够帮助设计者根据具体环境选择最合适的参数配置，以达到最佳的通信效果。这篇研究论文提供了一个重要的技术进步，它不仅展示了DCSK-ARQ/CARQ系统在多径衰落环境中的优势，也为其他类似系统的设计和优化提供了有价值的参考。通过理论和实践的结合，这篇文章为未来无线通信领域的抗衰落通信技术发展奠定了坚实的基础。

FANG et al.: DESIGN AND ANALYSIS OF A DCSK-ARQ/CARQ SYSTEM OVER MULTIPATH FADING CHANNELS 1639

Fig. 2. Block diagram of the GML detector for .

Fig. 3. BER results of the MA DCSK system, CSK system, and DS-SS system

over a multipath Nakagami fading channel. The parameters used are

, , , ,and .

corresponding to , is the th element of ,and is

the channel fading gain of the

th path corresponding to .

Next, the generalized maximum likelihood (GML) detector

[30] will be utilized to retrieve the source information

,whose

structure is illustrated in Fig. 2. Referring to this ﬁgure,

According to Section I, the DCSK system is superior to

the CSK and DS-SS system in terms of error performance

and implementation complexity. To validate this conclusion,

we present the BER results of the MA DCSK system, CSK

system, and DS-SS system in Fig. 3, where the frame length is

assumed as

and -sequences are used to implement

the DS-SS.

To simplify the comparison, the ARQ/CARQ and

CC techniques are not considered here. As can be observed, the

CSK and DS-SS systems, which possess similar error perfor-

mance, outperform the DCSK system in the low-SNR region

because of using a coherent detector, but they are inferior to

the DCSK system in the high-SNR region. In addition, the

performance advantage of the DCSK scheme will be more

remarkable as

increases due to a stronger robustness against

channel imperfection. Thereby, the DCSK system appears to

be a better SS scheme with respect to the other two systems.

2) DCSK-CC System : Consider a 2-user MA DCSK-CC

system [6], in which each transmission period is split into

two phases, i.e., broadcasting phase and cooperative phase. In

the 1st phase, the

th user broadcasts its own

DCSK signal

to the remaining terminals, i.e., the other user

and destination . In the 2nd phase, helps

For the sake of fair comparison, an extra “0” is added at the end of the pro-

duced

-sequence because the length of an -sequence is always odd.

Fig. 4. The system model (a) and the transmission mechanism (b) of the MA

DCSK-ARQ scheme. The transmission channels and the feedback channels are

denoted by solid lines and dashed lines, respectively.

to forward its messages to . Exploiting the decode-and-for-

ward (DF) protocol,

ﬁrstly decodes the received signal in the

2nd phase. Then, the retrieved information is re-modulated and

forwarded to

if it has been successfully decoded; otherwise,

remains idling. Beneﬁting from the cooperative diver-

sity, the DCSK-CC system achieves remarkable performance

improvement as compared to the DCSK-NC system at the

expense of sacriﬁcing some throughput. The above-mentioned

DCSK-CC system can be generalized to the

-user scenario,

in which a primary user transmits its signal to

aidedbythe

remaining

users (i.e., relays). For more comprehensive

knowledge of the DCSK-CC system, please refer to [6].

B. DCSK-ARQ/CARQ System

1) DCSK-ARQ System: The system structure of the MA

DCSK scheme with ARQ (DCSK-ARQ scheme) is presented in

Fig. 4(a), which includes

users (i.e., )

and one destination

. As seen from Fig. 4(b), the ARQ protocol

in the DCSK-ARQ system is implemented by a frame-by-frame

acknowledgement mechanism [23]. To be speciﬁc, the

users

ﬁrstly transmit their corresponding data-frames modulated

by DCSK (i.e., DCSK-modulated frames) to

simultane-

ously, where the frame length is deﬁned as

. Utilizing the

GML detector,

retrieves the DCSK-modulated frame cor-

responding to

and checks whether the

decoding is successful or not. If the decoding is successful,

an acknowledgement (ACK) message will be fed back to

while a negative-acknowledgement (NACK) message will be

fed back otherwise.

keeps retransmitting the current frame

rather than transmitting the next frame until an ACK message

of the current frame is received or the maximum number of

retransmissions (i.e.,

) is reached. As a result, there

are totally one transmission phase and at most

retrans-

mission phases in each transmission period. In this paper, it is

assumed that all the feedback channels used for transmitting the

ACK/NACK message are error free as in [23], [24]. In fact, the

feedback message can be protected by error control techniques,

e.g., error-correction coding, to realize reliable transmission.

Accordingly, this hypothesis is commonly made in most ARQ

research papers [25]–[29].

2) DCSK-CARQ System: Based on the DCSK-CC system,

we further propose a MA DCSK-CARQ system. As illustrated

in Fig. 5(a), the DCSK-CARQ system comprises one user

relays (i.e., and ),

and one destination

. Similar to the DCSK-ARQ system, each

transmission period also includes one transmission phase and

at most

retransmission phases in the CARQ protocol. In

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