基于设备能耗分簇的M2M通信随机接入方法

针对机器对机器(Machine to Machine, M2M)通信设备数量的持续增大导致M2M通信在当前蜂窝网络架构下会产生网络拥塞和接入成功率下降的问题,提出了一种基于设备能耗率分簇的M2M通信随机接入方法。该方法中M2M通信设备根据自身能量消耗率划分优等簇,即能耗率越大其优等级越高,优等级高的簇内设备享有随机接入资源的优先分配权,其随机接入资源由每簇的簇头代表簇接收,并在簇内设备之间通过随机接入竞争过程实现分配。仿真结果表明,相对于接入级限制(Access Class Barring, ACB)方法,该方法在接入成功率方面提升约5%,在延迟方面降低约10 s,能够有效降低设备能耗,提高设备接入的成功率。     

LTE TDD系统随机接入过程研究

随机接入技术是移动通信系统中UE与网络建立连接,进行通信的首要步骤,设计一种快速有效的随机接入过程将对系统的性能具有重要的意义。首先对LTE系统随机接入技术的进展情况进行了介绍,然后重点介绍一种基于LCR TDD帧结构的随机接入过程,给出接入流程。最后对碰撞概率进行定量分析。     

长期演进系统中随机接入信号的产生方法

提出一种适用于长期演进系统的物理层随机接入信号产生方法。基于ZC序列、SC-FDMA原理和基带信号产生等随机接入的主要技术,利用基于上采样和低通滤波的实用方法产生随机接入信号。复杂度分析和仿真结果表明,该方法能够降低信号产生的复杂度,其产生的信号与直接使用快速反傅里叶变换产生的信号非常接近,可以直接应用于实际系统。     

支持机器类型通信的动态接入拦截方法

对提升机器到机器(M2M)通信的接入成功率进行研究,在分组接入拦截(ACB)方案的基础上,提出一种加入自适应调整机制的改进方法。应用近似最大后验概率(AMAP)算法对等待接入的机器设备(MDs)数做出比较准确的估计,基于这种估计动态地调整ACB拦截参数,强化对负载和接入尝试的控制,提升对先导序列资源的利用率和接入成功率。仿真结果表明该方法可行有效。     

一种TDD-LTE随机接入检测算法

为了提高TDD-LTE上行链路随机接入信道处理的高效性,提出一种基于欠采样时域分步处理的随机接入检测算法。与传统方法相比,降低了运算的复杂度,同时分步处理的调度机制提高了接入响应的实时性。实验结果表明,在不同的信道环境下,该算法都具有良好的检测性能。     

基于LTE的物理随机接入信道前导检测研究

LTE系统中,物理随机接入信道(PRACH)的前导检测是整个随机接入过程的关键,提高前导检测的正确性是随机接入的主要任务之一。基于LTE FDD系统采用不同的子帧配置来提高物理随机接入信道前导检测的正确概率。仿真实验结果表明,不同的子帧配置能够影响正确检测概率,但要达到一定的信噪比时才能够得到给定的正确检测概率,从而满足用户所需的随机接入性能要求。     

LTE-A系统中物理随机接入信道信号检测的仿真与实现

根据多普勒频移对物理随机接入信道（PRACH）信号检测产生的影响进行分析,划分出了中速、高速、超高速三种模式,并提出相应改进的信号检测算法。对中速模式,提出了基于频偏校正的前导检测算法;对高速模式,提出了多重滑窗峰值检测算法;对超高速模式,提出了基于整数倍子载波的频偏补偿前导检测算法。仿真结果表明,不同场景下PRACH信号通过加性高斯白噪声（AWGN）信道传输,接收端虚警率性能至少改善了3.8 dB;通过扩展典型城市信道模型（ETU）信道传输,虚警率性能至少提升了1 dB。与频域相关检测算法相比,所提算法提高了前导信号成功检测概率,减少了接入时延。     

LTE系统级仿真建模实现及其优化

长期演进（LTE）作为下一代移动通信系统,其整体性能需要在系统级仿真中评估。LTE系统的设计、建模以及实现方法对仿真平台的有效性有直接影响,而目前功能较全的平台一般仿真速度较慢,针对这一问题,给出了LTE系统级仿真平台建模框架,并利用CPU多核以及OpenMP并行计算技术,对平台中耗时较多的模块进行优化,显著地提高了系统的仿真效率。通过比较不同的调度算法评估了仿真平台的性能。该系统级仿真平台达到了3GPP对系统设计的要求,为LTE-Advanced的标准化工作奠定了基础。     

一种LTE系统中计算CFI值的方法*

重点研究了LTE系统中存在承载PDCCH(physical downlink control channel,物理下行控制信道)传输的信息冗余和PDCCH盲检效率较低的问题,提出了一种改进的计算CFI值的方法。该方法按照速率匹配值的降序为各个PDCCH分配1/2/4/8个CCE(control channel element,控制信道元素),再复用各个PDCCH。仿真结果表明该方法能够有效地消除冗余信息,减少PDCCH盲检的平均次数。     

LTE系统确认模式的设计与一致性测试*

为提高数据链路的可靠性,根据3GPP最新发布的标准,研究了AM传输模式的运行原理与实现机制,通过SDL和TYCN的协仿真进行协议一致性测试.测试结果表明该方案能较好地执行AM的相关功能,具有一定的实用价值.     

LTE PUSCH信道中HARQ-ACK/NAK信息编码算法*

针对LTE物理上行共享信道（PUSCH）,且HARQ-ACK/NAK信息比特数在1或2 bit时,提出三种HARQ-ACK/NAK信息编码算法。这三种算法的思想来源于重复码、线性分组码、汉明距离、欧式距离。比较三种算法的仿真结果,选择了一种在任何调制方式下都可以达到很高BER要求的最优编码算法,该算法已应用于LTE-TDD无线综合测试仪表的开发中。     

Dynamic LTE resource reservation for critical M2M deployments

Machine-to-machine (M2M) communications are envisioned to be major contenders for long term evolution (LTE) cellular resources in the time of fifth generation (5G) wireless communications and beyond. They will be used for a variety of applications on which users will rely for managing many aspects of their daily life. One of the promising fields in which M2M communications can play a major role is the field of emergency services. In such situations, it is crucial to ensure the reliable allocation of communication resources to M2M communications to ensure the right decisions and actions are taken in a timely manner. One of the techniques that could be used to ensure sustained and reliable resource allocation is to use an LTE-based virtual resource-slicing scheme. This scheme ensures a dynamic and an uninterrupted allocation of the resources dedicated to M2M communications in such a way that accommodates the changing needs of the emergency operations. In this paper, we introduce two schemes to allocate LTE resources to M2M emergency deployments in an adaptive manner. These schemes ensure that the resource allocation responds to the changing needs of the underlying emergency application. The adaptation period is also varied in response to the speed of change of the allocation requirements. This is done to ensure that the devices involved in critical missions are not competing for resources with the rest of network clients. We conduct several experiments to assess the success of the proposed schemes in responding to the needs of emergency M2M deployments.     

LTE系统自适应软频率复用技术研究

提高小区边缘用户性能是蜂窝移动通信系统的经典难题.下一代蜂窝移动通信系统3GPP LTE通过有效的小区间干扰协调以及频率资源分配来改善小区边缘用户性能.提出一种自适应软频率复用算法,根据系统负载情况自适应地为各小区分配主、副载波及其发射功率,在实现系统吞吐量优化的同时保证小区中心和边缘区域速率需求.算法首先通过穷尽搜索和贪婪递减策略,获得单小区最优资源分配,然后在不同小区间迭代执行单小区算法直到系统吞吐量不变为止.仿真结果表明,算法通过多次迭代后,系统吞吐量保持不变并输出一种优化的资源分配方案.与同类频率分配算法相比,可以有效提升小区边缘用户的吞吐量,同时获得更高的系统容量,更适用于高速率的LTE系统.     

LTE系统下行基于调度度量值的资源分配方案

在多业务的正交频分多址(OFDMA)蜂窝系统中,为改善小区整体的吞吐量并提高多用户之间传输数据的公平性,提出一种基于最优调度优先级进行资源块分配的长期演进项目(LTE)下行分配方案。打破传统资源分配过程中顺序分配资源的束缚,将用户与资源块(RB)配对,优先把服务质量最好的RB资源分配给相应的用户,尽量保证用户在各自有利的信道上传输数据。仿真结果表明,该方案在不增大丢包率的前提下,有效提高了系统的吞吐量和公平性指数,对LTE下行链路是一个很好的选择。     

MPSoC based on Transport Triggered Architecture for baseband processing of an LTE receiver

Wireless communication over LTE (long term evolution) brings several design challenges to industry and academia, due to its high throughput demand. Specially in the case of hand held mobile devices where the power budget is very limited and high throughput requires more computation power. On the other hand, the industry is struggling for flexible hardware solution, a Software Defined Radio (SDR), to amortize huge costs of hardware changes to suit the continued evolution in wireless standards. In this article, an MPSoC design has been presented for the baseband processing of a 20 MHz LTE system. Transport Triggered Architecture (TTA) has been preferred over conventional DSPs/VLIW architectures as processing element (PE) of MPSoC. Processing tasks are statically scheduled. Synchronization among the PEs is based on polling of a shared memory space. In addition an approach is presented to organize I/O buffer in such a way that the stalling probability of a PE should be reduced to exploit efficiently data and task level parallelism. The total power consumption by all the PEs synthesized on 130 nm technology at 200 MHz and 1.5 V is 105.04 mW. The total energy consumption to process one subframe including carrier recovery is 0.0767 mJ. Our study shows that TTA architecture brings several improvements in conventional SIMD/VLIW architectures. TTA as contrary to other run time designs has a guaranteed performance and lower energy consumption due to the fact that all the data dependency/independency issues are resolved at compile time. Further, it is also true due to the fact that TTA has a reduced register file (RF) traffic, number of RF ports and lower overall cycle count for a given task. To the best of author’s knowledge this article is among the first few published articles on LTE receiver implementation with published figures like time, frequency, power and perhaps the first article explaining further in detail about data access pattern to process an LTE subframe, memory organization, subsystem interconnection, and synchronization.     

一种基于空中接口和核心网协同的LTE系统密钥推演方法

从窃听方的角度, 基于空中接口与核心网协同的思想提出了一种LTE系统密钥推演方法。首先, 在实现根密钥同步的基础上, 根据空中未加密信息提供的安全算法列表, 遍历有限安全算法集; 然后, 将遍历的安全算法与获取的父密钥共同作为参数, 通过密钥生成函数生成空中接口子密钥; 最后, 通过比对明文和解密密文确定密钥。可行性分析表明, 窃听方可以利用该方法推演出空中接口子密钥; 误码率小于10^-3时, 可使密钥推演成功率达到90%以上, 具有实际应用意义。     

A Hybrid Offline-Online Approach to Adaptive Downlink Resource Allocation Over LTE

Radio resource management mechanisms in current and future wireless networks is expected to face an enormous challenge due to the ever increasing demand for bandwidth and latency sensitive applications on mobile devices. This is because an optimal resource allocation scheme which attempts to multiplex the available bandwidth in order to maximize Quality of service (QoS), will pose an exponential computational burden at eNodeB. In order to minimize such computational overhead, this work proposes a hybrid offline-online resource allocation strategy which effectively allocates all the available resources among flows such that their QoS requirements are satisfied. The flows are firstly classified into priority buckets based on real-time criticality factors. During the offline phase, the scheduler attempts to maintain the system load within a pre-specified safe threshold value by selecting an appropriate number of buckets. This offline selection procedure makes use of supervisory control theory of discrete event systems to synthesize an offline scheduler. Next, we have devised an online resource allocation strategy which runs on top of the offline policy and attempts to minimize the impact of the inherent variability in wireless networks. Simulation results show that the proposed scheduling framework is able to provide satisfactory QoS to all end users in most practical scenarios.