| 1. | Scan for downlink channel and establish synchronization with bs
用户端设备扫描下行信道，之后于基站建立同步。 |
| 2. | To meet the demand on broad band services , the methods providing dual downstream channel in one cmts were studied in this thesis
为了适应宽带化的需要，本文探讨在一台cmts中提供两个下行信道的方法。 |
| 3. | The downstream channel is a point - to - multipoint broadcasting channel with a wider bandwidth , while the upstream one is a multipoint - to - point share medium with a narrow bandwidth
Hfc网络下行信道采用一点对多点的广播方式，用户共享下行资源实现比较简单。上行信道是一个多点对一点的媒体共享信道。 |
| 4. | In the implementation , we used the multiprocessing method in qnx to analyze the general flow chart of system , and divided the realization of dual downstream channel into three modules
在具体实现上采用了qnx的多进程编程思想，对整个系统的流程进行了分析设计，将双下行信道的实现分为三个大的模块进行讨论。 |
| 5. | With regard to modulation , cablemodem adopts qam on downlink channels , and qpsk or the more superior s - cdma on the uplink to achieve a better suppression of noise interference
Cablemodem的下行信道采用了qam调制方式，而在上行信道上，为了更好地抑制噪声干扰，通常采用抗干扰性能较好的qpsk或者s - cdma调制技术。 |
| 6. | With amounts of flight experiment , proved the design could satisfy the demand of large quantities of data in down channel and high precision and reliability of control parameters in up channel
经大量完全自主飞行实验结果表明，所设计的监控系统软件不仅能够满足小型无人机下行信道传输数据量大的监测要求，而且可以确保上行信道控制参数高精度、高可靠性的要求。 |
| 7. | Down link channel of new generation space tt & c system generally select qpsk as its modulation mode . firstly , carrier synchronization of qpsk is studied in the thesis , and then the key question - carrier synchronization in low snr and severe doppler frequency shift is systemic analyzed . in addition , different existing project are analyzed and compared
新一代航天测控系统的下行信道一般选择qpsk作为其信号调制方式，本文首先研究了qpsk的载波同步问题，对其中的关键问题? ?低信噪比及大多普勒频移情况下的载波同步进行了系统的分析，对现有的不同方案进行了分析与比较。 |
| 8. | Traditional delay estimation based on ica requires the trail sequences to initialize the receiver , but the new algorithm based on ica does not need the trail sequences . it is based on the channel character of downlink , using the ica algorithm to estimate the multi - path mixture matrix , then , find the delay information which is embodied by the column vector of the mixture matrix . the simulation results show that it does enhance the performance of traditional detector without wasting the invaluable frequency resource
传统的信道估计算法需要训练序列使接收端的参数调整到理想状态，而本文提出的基于ica的信道估计的多用户检测算法不需要训练序列，它是利用下行信道的固有特点，用ica的盲源分离法估计出多径信道的卷积矩阵，从而从中提取出信道的延迟信息，仿真实验结果证明这种方法在节省了频谱资源的同时取得较好的估计效果，使得传统的接收机的误码性能得到了很大的提高。 |
| 9. | In this paper , the hybrid - fiber - coax network ' s topology , architecture , characters of the channel , and the network service were plenty studied . after anatomizing docsis protocol , we point out the disadvantage of single downstream channel , and discuss the realization of dual downstream channel
本论文首先对hfc网的拓扑结构、体系结构、信道特点和网络业务等方面进行了充分的研究，然后在对docsis协议细致分析的基础上，指出了目前实际工作中单下行信道的弊端，讨论了多下行信道的实现方法。 |
| 10. | In this paper , after introduction of the code division multiple access ( cdma ) and orthogonal multicarrier ( mc ) technique , the system model of mc - cdma is analyzed and the bit error rate ( ber ) performance in downlink and uplink channel is shown in awgn channel by computer simulation
本文在码分多址技术和正交多载波技术原理基础上，分析了高斯白噪声信道中多载波码分多址( mc - cdma )系统的数学模型，并且使用不同的扩展码对下行信道和上行信道误码率性能分别作了计算机仿真分析。 |
