随着移动数据业务的快速增长，传统的蜂窝系统或单纯提高传输速率已无法满足未来无线通信的需求。一系列有别于传统无线网络的新型网络架构在学术界和工业界内得到广泛的关注，其中认知无线电网络引入节点的认知功能，可以有效地提高频谱利用率和用户传输效率；Ad Hoc网络作为一种分布式、自组织、具有良好移动性能的无线网络，适用于需要快速建立通信的环境。上海交通大学无线所的相关研究如下：

With the rapid growth of mobile data services, the traditional cellular system is unable to meet the demand of future wireless communications. A series of infrastructure-less wireless network architectures have received extensive attentions from both academic and industry fields. Among them, cognitive radio networks, which introduce the cognitive function to nodes, can effectively improve the spectrum utilization and the transmission efficiency. Due to the nature of decentralization and self-organization, Ad Hoc networks are suitable for a variety of applications where the central nodes cannot be relied on. Researchers at the IWCT of SJTU have made the following theoretical advances in the areas of infrastructure-less wireless networks.

双向中继

双向中继是结合了网络编码的无线协作通信基本单元。其核心是在两数据节点经中继协助相互传递信息时，由中继将两路数据合并，然后同时广播给接收端。相对于传统中继技术，双向中继能显著提升频谱效率。我们取得的主要相关成果包括：

1)提出了针对不对称信道的新型物理层网络编码方案，性能明显优于现有方案，而且更逼近容量域；

2)首次分析了保证业务统计时延需求的有效容量，并提出了跨层资源优化算法;

3) 提出了成对校验译码算法，实现了衰落信道下基于LDPC码的信道-网络联合编译码；4)在多天线环境下，还设计了基于最小均方误差的源节点和中继节点联合预编码。

Two-Way Relaying

Two-way relay channel, where two source nodes exchange information with each other the help of a relay node, is a building block of wireless networks to apply network coding in the physical layer. Compared with traditional one-way relay techniques, two-way relaying is able to achieve much higher spectral efficiency. We have made tremendous progress in two-way relaying as follows.

1) We proposed a novel physical layer network coding scheme, named Superimposed XOR, for asymmetric two-way relay channels. It is superior than existing methods and closely approaches the capacity bound.

2) We studied the effective capacity of two-way relay systems for statistical delay QoS guarantees, and proposed an optimal cross-layer resource optimization algorithm.

3) For LDPC-coded two-way relay fading channels, we introduced pairwise check decoding at the relay to realize joint network-channel coding.

4) When each node is equipped with multiple antennas, we also designed joint source and relay precoding based on MSE criterion.

动态频谱检测与认知接入

对频谱的动态检测可以迅速地发现空闲频率，提高频谱利用率；对传输链路的认知能够显著提高用户的接入效率，提高网络的吞吐量和能量效率。我们对动态频谱检测的快速算法和高能效认知接入展开了深入的研究，取得主要成果包括：

1. 循环谱域噪声统计分析：首次建立了循环谱域信号检测门限和漏检概率之间的关系，并根据特征循环频率处的噪声统计特点，提出了快速循环谱域频谱检测算法。
2. 高能效认知接入方法：通过对认知终端子模块的能耗建模和动态频谱分割单元的优化，设计了能量效率最优的认知网络信息共享方式。

Dynamic Spectrum Sensing and Cognitive Access

Dynamic spectrum sensing is used to find the idle channel as quickly as possible. Cognition of the transmission link can significantly improve the transmission efficiency, network throughput and energy efficiency. We study the fast algorithms for dynamic spectrum sensing and cognitive access with high efficiency. The main results are as follows.

1) Statistical Analysis in Circle Noise Spectral Domain. We are the first to establish the relationship between the detection threshold of circle spectrum signal and the probability of false alarm. We further propose a fast detection algorithm for circle spectral domain based on the noise statistics characteristics.

2) High Energy-Efficient Cognitive Access Method. We design the optimal Energy-Efficient information sharing method for cognitive network by constructing the energy consumption model for cognitive terminals and optimizing the dynamic spectrum division unit.

动态频谱分配机制和认知无线电系统容量提升

如何有效地进行动态频谱分配是认知无线电领域内趋待实现的一个关键技术。在工信部重大专项

等资助下，对动态频谱分配机制和认知无线电系统容量提升进行了深入研究，取得的主要成果包括：

1） 提出基于经济学理论的认知无线电动态频谱分配方案，广泛研究了基于博弈、拍卖、契约等理论的频谱交易机制，为认知无线电技术在实际网络环境中的应用提供参考。

2） 提出移动多播（MotionCast）的机制，提高数据复用率；建立集群拓扑模型，解决异构网络的最优连接性、覆盖性。

Dynamic Spectrum Allocation Mechanism and Capacity of Cognitive Radio Networks

Efficient dynamic spectrum allocation is a key technology in wireless domain waiting for realization. We study the dynamic spectrum allocation mechanism and the capacity improvement of cognitive radio system. The main results obtained are as follows.

1) We proposed cognitive radio dynamic spectrum allocation schemes based on economic theories. Extensive researches include game theory, auction and contract theory, providing reference for practical application of cognitive radio technology in actual network environment.

2) We proposed motion cast mechanism to improve the reuse rate of data. We also established clusters topology model, and solve the optimal connectivity and coverage in heterogeneous networks.