Analysis and Simulation for Capacity of Time Division-Synchronous Code Division Multiple Access System

Capcity both in uplink and downlink of TD-SCDMA (time division-synchronous code division multiple access) system is studied in a multi-cell environment. The theoretical expressions of the mean of intercell interference in uplink and the mean of sum of power allocation in downlink are given, by which uplink and downlink capacity is analyzed. Furthermore, we give the simulation models for both uplink and downlink capacity. The results from theoretical analysis and simulation fit very well. In the end, the maximum number of users that TD-SCDMA system can serve for 12.2 k speech service is given.

A passive optical network based on optical code division multiplexing and time division multiple access technology

A passive optical network （PON） scheme based on optical code division multiplexing （OCDM） for the downstream traffics is proposed and analyzed in detail. In the PON, the downstream traffics are broadcasted by OCDM technology to guarantee the security, while the upstream traffics pass through the same optical fiber by the common time division multiple access （TDMA） technology to decrease the cost. This schemes are denoted as OCDM/TDMA-PON, which can be applied to an optical access network （OAN） with full services on demand, such as Internet protocol, video on demand, tele-presence and high quality audio. The proposed OCDM/TDMA-PON scheme combines advantages of PON, TDMA, and OCDM technology. Simulation results indicate that the designed scheme improves the OAN performance, and enhances flexibility and scalability of the system.

Joint power control based on service factor for code division multiple access system

An important feature of the traffic in mobile networks is burstiness. Drawbacks of conventional power control algorithms for time division duplex （TDD）-code division multiple access （CDMA） systems are analyzed. A joint power control algorithm based on service factor is presented to address the TDD-CDMA mobile services in the burst mode according to the Markov modulated Bernoulli process. The joint power control equation is derived. A function model is developed to verify the new algorithm and evaluate its performance. Simulation results show that the new power control algorithm can estimate interference strength more precisely, speed up convergence of power control, and enhance power efficiency and system capacity. It is shown that the proposed algorithm is more robust against link gain changes, and outperforms the reference algorithms.

Space-division multiple access for CDMA multiuser underwater acoustic communications

Time reversal mirror （TRM） can use the physical characteristics of the underwater acoustic （UWA） channel to focus on the desired user in multi-user UWA communication. The active average sound intensity （AASI） detector can estimate all azimuths of users with the same frequency band at the same time in order to achieve directional communication by vector combination. Space-division multiple access （SDMA） based on TRM combined with the AASI detector is proposed in this paper, which can make the capacity of the code division multiple access （CDMA） UWA system significantly increase. The simulation and lake test results show that the 7-user UWA multi-user system can achieve low bit error communication.

Hybrid Deep Learning-Based Adaptive Multiple Access Schemes Underwater Wireless Networks

Achieving sound communication systems in Under Water Acoustic(UWA)environment remains challenging for researchers.The communication scheme is complex since these acoustic channels exhibit uneven characteristics such as long propagation delay and irregular Doppler shifts.The development of machine and deep learning algorithms has reduced the burden of achieving reli-able and good communication schemes in the underwater acoustic environment.This paper proposes a novel intelligent selection method between the different modulation schemes such as Code Division Multiple Access(CDMA),Time Divi-sion Multiple Access(TDMA),and Orthogonal Frequency Division Multiplexing(OFDM)techniques using the hybrid combination of the convolutional neural net-works(CNN)and ensemble single feedforward layers(SFL).The convolutional neural networks are used for channel feature extraction,and boosted ensembled feedforward layers are used for modulation selection based on the CNN outputs.The extensive experimentation is carried out and compared with other hybrid learning models and conventional methods.Simulation results demonstrate that the performance of the proposed hybrid learning model has achieved nearly 98%accuracy and a 30%increase in BER performance which outperformed the other learning models in achieving the communication schemes under dynamic underwater environments.

A timeslot assignment scheme for cluster-tree based wireless sensor network

Many efforts have been made to develop time division multiple access （TDMA） slots allocation in a multi-hop converge-cast wireless sensor network （WSN）, however, most of them either use complex algorithm or concern frames only without simultaneous transmission in a single slot. In this paper, we present a timeslot assignment scheme for cluster-tree-based TDMA WSN, co：＇ering three frequently used working modes in practical applications. The shortest frame formed can guarantee real-time conununication and is also facilitated for message and slot integration, since timeslots allocated to a single node are continuous. During allocation processes, the algorithms are distributed and light-weighted. The experiment resulted from a WSN prototype system shows that our scheme can achieve a good reliability.

Adaptive blind gain correction of time-interleaved ADCs forwide-band communication applications

High spectral efficiency is essential in design of multimedia communication systems such as L-band mobile in addition to various requirements of transmission quality. Time-interleaved A/D converter （TI-ADC） is an effective candidate to implement wide-band ADC with relatively slow circuits accounting for digital spectrum management. However, practical performance of TI-ADC is largely limited because of mismatches between different channels originated from manufacturing process variations. In this paper, a blind adaptive method is proposed to correct gain mismatch errors in TI-ADC, and it is verified through simulations on a two-channel TI-ADC. In proposed method, gain mismatch error is estimated and corrected in an adaptive scheme. Proposed compensated T1-ADC architecture is structurally very simple and hence suitable for realiza- tion in integrated circuits. Besides, proposed digital compensation algorithm not only is computationally efficient but also provides an improvement of 32.7 dB in the performance of two-channel TI ADC.

SIMPLE AND EFFICIENT SPACE-TIME CHANNEL AND DOA ESTIMATION TECHNIQUES IN TD-SCDMA SYSTEMS

In this paper, a simple method is presented for multi-user space-time channel estimation in Time Division-Synchronized Code Division Multiple Access (TD-SCDMA) systems. The method is based on a spe- cific midamble assignment strategy, which results in a cyclic Toeplitz midamble-matrix in the linear equation of the received data vectors. A Fast Fourier Transform (FFT)-based algorithm is used to obtain the estimate of the uplink multi-user space-time channels. Furthermore, the estimated space-time channel is applied to the identification of multi-paths for each user, and Direction Of Arrival (DOA) estimation for each path is carried out by using the extracted spatial signature vector. Aside from the simplicity in computation, the proposed di- rection of arrival estimation method can effectively resolve multi-paths regardless of the correlation and angle separations of the multi-paths.

Development of Recovery and Redundancy Model for Real Time Wireless Networks

The growth in wireless technologies applications makes the necessity of providing a reliable communication over wireless networks become obvious.Guaranteeing real time communication in wireless medium poses a significant challenge due to its poor delivery reliability.In this study,a recovery and redundancy model based on sequential time division multiple access(S-TDMA)for wireless communication is developed.The media access control(MAC)layer of the S-TDMA determines which station should transmit at a given time slot based on channel state of the station.Simulations of the system models were carried out using MATLAB SIMULINK software.SIMULINK blocks from the signal processing and communication block sets were used to model the communication system.The S-TDMA performance is evaluated with total link reliability,system throughput,average probability of correct delivery before deadline and system latency.The evaluation results displayed in graphs when compared with instant retry and drop of frame were found to be reliable in recovering loss packets.

宽带跳频TDMA辐射源网群的定位及网群划分方法

为了解决现有方法难以对宽带跳频时分多址(frequency hopping-time division multiple access,FH-TDMA)辐射源网群定位的问题,提出一种仅利用波达方向(direction of arrival,DOA)信息的多站定位及网群划分方法。首先通过模拟滤波对各站接收到的信号进行频段划分,通过基于多相滤波的数字信道化方法把信号输出到多个信道中;然后通过直接定位(direct position determination,DPD)算法计算得出各时隙辐射源的位置;最后先通过不同参数的基于密度的噪声应用空间聚类(density-based spatial clustering of applications with noise,DBSCAN)算法选择出最佳的辐射源定位结果,再根据提出的基于先验信息的改进K-means聚类算法进行网群划分。所提方法实现了采样率和信号处理速率的降低,且无需站间严格的时间同步。结果表明,所提方法有效估计出了辐射源的数量、位置,以及网群划分情况。

基于四阶相关的时分多址调制数据独特码盲识别

针对非合作通信中时分多址(TDMA)信号的独特码(UW)盲识别问题,该文首次提出分布式独特码的盲识别算法。区别于比特层的独特码识别算法,该文分别针对集中式独特码和分布式独特码,提出面向调制数据不同窗口之间相关性的波形层独特码识别算法。算法利用独特码的一致性与相关性,分两步进行,首先通过差分累积消除不同突发信号间频偏与相偏的影响,来纵向对齐各个突发信号的独特码,然后通过多层差分共轭4阶相关算法识别出独特码的位置和长度。仿真分析了不同突发个数、信噪比和有无频偏相偏情况下算法的性能,验证了波形层识别独特码的有效性,针对集中式独特码和分布式独特码,所提算法在信噪比为5 dB时均达到了95%以上的识别率,具有一定的工程应用价值。

基于DRL的定向网络时隙复用和功率控制协议

近年来,无人机网络逐渐地广泛应用于各行各业,对无人机网络能提供的网络容量提出了更高的要求。定向天线结合无人机网络构成定向无人机网络以增加网络资源应对无人机网络中各个节点对网络有限通信资源的竞争造成网络容量低的问题。定向无人机网络通过定向天线的空间复用能力可以提高网络的时隙利用效率。针对TDMA协议在定向组网中时隙利用率过低导致网络容量受限的问题,该文提出了一种基于深度Q网络(DQN)的定向无人机网络时隙复用和功率控制协议。为了提高时隙利用率,考虑在单位时隙进行多个链路通信以实现时隙资源的复用。然而多个链路在同一个时隙通信会产生链路间的干扰,如何在考虑链路间相互干扰的情况下控制功率提高网络的容量是时隙复用研究的重点问题。为了解决该问题,首先考虑以功率要求和每条链路最小信道容量为约束,考虑相较于其他研究更为复杂更符合实际的链路互干扰模型,建模问题为最大全网容量问题。然后为了构建链路间的更复杂的互干扰环境,将多个链路的瞬时信道信息、定向增益状态融入到DQN框架的状态中,DQN的奖励为高于最小信道容量的链路信道容量的和。最后,将每个时隙的优化问题扩展到每一帧的优化问题,并利用多个DQN进行求解。仿真结果表明,在保证每个被分配时隙的最小信道容量前提下,相较于对比方法网络容量有了很大的提升。

含网关节点的高时隙复用率TDMA协议

针对网络收敛慢、拓扑表不完整时导致的信道冲突以及空闲时隙浪费问题,提出一种提高节点时隙利用率和网络可靠性的多跳时分多址接入协议。该协议提出3种新机制,使用时隙请求时期快速收敛机制,加快时隙请求时期的收敛;使用空闲时隙公平重用机制,消除中心节点调度时隙碰撞问题,提高空闲时隙利用率;使用一跳邻居多层次调度机制,降低数据重传的时延。仿真结果表明,在时隙请求时期收敛时间、数据传输平均时延及数据传输成功率方面,该协议较现有协议性能更优。

基于预约机制的RFID防碰撞安全认证协议

为解决RFID领域中多标签识别存在的信息泄露和信息碰撞问题,提出了一种基于预约机制的防碰撞安全认证协议(reservation mechanism for authentication protocol,RMAP)。RMAP可有效抵御窃听、重放、欺骗等攻击,且采用精简杂凑运算次数的方法,有效地简化了计算量。同时,采用载波监听多点接入技术,通过重传随机数进行帧序号的二次预约和重排,实现标签的无碰撞有序通信和识别效率的最优,解决了现有协议为避免信息碰撞而对标签进行循环性识别导致的识别效率低、读取时间长的问题。对RMAP识别效率的数值分析表明,当待识别标签数量少于1024时,RMAP的最低识别效率为95.15%,高于常用防碰撞协议。

基于置零干扰抵消的水声移动多用户通信技术

文章对变换域置零干扰抵消算法进行了改进,使其适用于水声移动多用户通信系统,并将置零干扰抵消算法与多通道合并技术相结合,通过引入空间处理增益进一步克服多用户通信系统中的多址干扰。仿真结果表明,该算法在2用户场景,信干比为-10 dB的条件下,能够有效克服干扰用户的干扰,在误码率达到10^(-4)时,其性能曲线与无干扰情况下接收性能曲线相差1 dB左右,与传统串行干扰抵消算法相比,改进后的置零干扰抵消算法在水声移动场景下表现更佳。经过湖试数据测试,在3用户系统中,利用改进后的置零干扰抵消算法使多址干扰得到了有效抑制,期望用户的输出信噪比较处理前提高了约8 dB,证明了该算法的有效性。

基于TDD的低轨卫星跳波束资源分配算法

低轨(LEO)卫星跳波束技术可以灵活分配系统资源,适用于业务分布不均匀的场景。时分双工(TDD)方式可以减少星载和地面终端设备的天线数量,有效降低其复杂度,并有利于开展上下行非对称业务。本文提出一种基于TDD的LEO卫星跳波束资源分配算法,在满足业务需求的基础上,以最小化时域资源消耗为目标,建立支持跳波束和多频时分多址接入(MF-TDMA)机制的LEO卫星反向链路资源分配模型;综合考虑星地动态时延补偿,采取一种多层次的跳波束时隙架构设计,以最大化可用时隙为目标,建立上下行时隙切换模型,并提出一种基于TDD的跳波束时隙排布优化方法。仿真结果表明,对比于传统的MF-TDMA资源分配方法或固定多波束均分算法,本文提出的算法能有效提高系统的时隙利用率和吞吐量。

一种主从式卫星集群的星间组网系统设计

为解决主从式卫星集群在离散稀疏拓扑下的组网通信问题,保障其星间实时交互遥控遥测及任务信息的需求,根据主从式卫星集群的分层、分簇的空间拓扑特点,本文提出了一套通信系统架构和星间组网协议栈的设计方案。首先,在网络层的设计上,给出了网络层的数据结构、基于多权重优先级代价函数的子网簇首选择备份机制以及子星建网入网的流程;其次,在数据链路层,根据分包遥控和分包遥测体制按照层次化对数据进行处理;然后,在物理层的设计中采用扩跳频作为星间链路的通信体制,采用时分多址方式实现卫星集群的多用户通信,并给出了星间链路的具体通信指标;最后,对星间通信进行了链路计算,计算结果表明物理层设计满足各星通信需求。

直升机自适应扁平组网技术研究

当前,训练网络通常采用“地面基站-终端”的中心化网络结构。文章通过对比分析中心化和去中心化网络结构的优缺点,针对直升机训练中的无疆域需求,提出了一种自适应切换的扁平网络结构。该结构可以根据中心节点的状态实现网络模式的切换,利用互同步、按需路由及动态资源分配等方案设计,实现直升机空中通信终端和地面通信终端之间的无线通信传输,以及网络的随时接入。

一种无线机控器复示器及其调车作业系统

在广泛调研当前铁路中间站使用本务机车进行调车作业情况基础上,针对中间站本务机调车作业中司机劳动强度大、作业效率低,以及存在较大安全隐患的问题,设计出一种无线机控器复示器和调车作业系统。详细阐述无线机控器复示器的构成、功能、基本工作原理,以及空中接口通信可靠性和时序控制等关键技术;介绍基于机控器复示器的调车作业系统作业流程。现场试验和对试验结果的分析表明,基于机控器复示器的平面调车作业系统,能够大大降低司机的劳动强度,提高调车作业效率,有效保障调车作业安全,对保障铁路安全生产具有积极意义。

基于多波束GEO卫星的宽带移动通信系统

提出基于多波束天线静止地球轨道卫星的宽带移动通信系统方案,与常规结构同类系统用户相比,其容量更大、业务质量更好。采用时隙同步码分多址辅助的多频时分多址接入、程控交换与因特网协议交换结合的交换、时分复用和准正交时分复用下行链路传输体制,可显著增加用户量,简化星上设备,改善互联网应用业务质量。用户接入信道数为173 880,最高用户下载速率达155 Mbps。仿真结果表明,140个波束、每波束26个16幅度相移键控信号的用户下行链路传输比频分复用传输的链路性能改善11.65dB,使得宽带用户"动中通"天线等效口径缩小至原来的1/4,成本大幅降低。