Piecewise companding transform is a flexible and efficient way to solve the high peak-to-average power ratio (PAPR) problem for orthogonal frequency division multiplexing (OFDM) systems. A novel threshold-based piecewise companding transform is proposed in this paper. Based on the statistical characteristics of amplitudes, OFDM signals are classified into three groups (i.e., small, average and large signals). Different from conventional approaches, two dedicated designed thresholds are set to amplify the small signals and compress the large signals, respectively. Simulation results verify the improvement in PAPR reduction of the proposed scheme. Moreover, a lower bit error rate (BER) performance loss can be obtained by introducing the iterative detection with a moderate increase in complexity.
针对Euclidean Geometry(EG)-LDPC码码字的循环特性以及FWBF(fast weighted bit flipping)算法的算法结构设计高速LDPC译码器。具体实现方法如下:首先通过对RAM进行合理的划分,赋给不同的RAM相应的规则号和初始地址值保证数据的无冲突存取,然后通过向量化操作实现运算数据的高速存取。此外,校验式品质计算模块通过引入一种新型的树形搜索电路来降低该模块的功耗和延迟。最后,对EG255码采用5路并行模式,在Cyclone III EP3C120F780C7芯片上实现,信息吞吐量可达75.98Mbs,占用芯片逻辑资源不超过23%,RAM资源不超过4%。
根据网络拓扑结构认知网络可分为有中心控制设施的网络和认知Ad-hoc网络(CR Ad-Hoc Networks,CRAHNs).在CRAHNs中,由于无法预知主要用户(Primary User,PU)何时占用信道次要用户(Secondary User,SU)不能使用固定的公共控制信道(Common Control Channel,CCC).针对这种情况,提出一种交会跳频算法通过设计分布式的CCC方案使次要用户短时间内交会在共同的可用信道上,并建立通信链路.将文中提出的算法与其他同类算法比较后发现,文中算法提供的交会时间(Time To Rendezvous,TTR)最小.
