免许可频段SA LTE-U系统的随机接入和资源定位技术研究

发布时间：2018-10-08 20:32

【摘要】：独立模式的免许可频段的长期演进(Standalone Long-Term Evaluation in Unlicensed band,SALTE-U)系统是缓解许可频段资源稀缺和移动数据流量激增矛盾的主流解决方案之一。然而,SALTE-U系统与无线局域网(Wireless Local Area Networks,WLAN)在免许可频段上竞争时频资源,使得其信道时间上非连续、单次占用时长有限且再次信道占用时刻无法预知,造成用户的资源时域位置失效、随机接入的交互过程频繁出错、用户积累引发的冲突加剧、随机接入冲突解决能力和上行数据传输能力之间难以兼顾。本学位论文研究SALTE-U系统中的资源定位、随机接入和数据传输,设计可操作的方案和协议,给出冲突控制方法和资源分配优化方法,进行性能分析。针对SALTE-U系统的资源定位失效问题,研究面向信道非连续和时间不确定条件下的资源定位方法。我们提出有效信道和有效帧号的概念,以排除信道的时间不确定性带来的影响。我们设计有效帧号的生成方法和更新规则,给出有效帧号的搭载位置和解析方法,推导关于有效帧号的资源定位表达式,以保证计算得到的资源时域位置始终落在信道占用时段中且子帧类别始终正确。我们给出资源定位的性能指标和统计公式,并验证所提方案的有效性。针对SALTE-U系统随机接入冲突严重和信道非连续条件下现有随机接入协议不可用的难题,研究新的随机接入协议和冲突控制方法。我们设计一种基于有效信道和有效窗长的随机接入协议,避免因本系统的信道资源特点导致交互过程难以完成和用户长期滞留在随机接入过程,以提高系统性能和信道利用率。我们提出重传概率指数衰减的冲突控制方法,以缓解因信道断续造成的用户在非信道占用期间大量积累而在信道占用期间同时发起随机接入过程导致的剧烈的用户冲突。定义接入率、重选率和平均时延这三个性能指标,用于衡量随机接入的性能。进行性能分析,推导得到上述性能指标的表达式。进而验证所提随机接入协议和冲突控制方法的有效性。针对SALTE-U系统的随机接入冲突解决能力和上行数据传输能力之间的矛盾,研究最优随机接入信道(Random Access Channel,RACH)数目配置方法。以随机接入成功概率和平均接入时延为约束,建立使可供数据传输的上行共享信道数目最大的优化问题。提出联合到达率估计和最大似然估计的用户数预测方法,得到关于当前用户数的解析式。提出最优RACH数目的求取算法,用于求解优化问题得到最优的RACH数目,从而实现冲突解决能力和上行数据传输能力之间的平衡。
[Abstract]:Long-Term Evolution (Standalone Long-Term Evaluation in Unlicensed band,SALTE-U) system with independent mode is one of the main solutions to alleviate the contradiction between resource scarcity and mobile data traffic surge in licensed frequency band. However, the SALTE-U system competes with the wireless LAN (Wireless Local Area Networks,WLAN) in the free frequency band, which makes the channel time discontinuous, the time of single occupation is limited and the time of channel occupation is unpredictable, which results in the time domain position of the user's resources being invalid. The interactive process of random access frequently goes wrong and the conflicts caused by user accumulation are aggravated. It is difficult to balance the conflict resolution ability of random access and the ability of uplink data transmission. This thesis studies the resource location, random access and data transmission in SALTE-U system, designs operable schemes and protocols, gives conflict control methods and resource allocation optimization methods, and analyzes the performance. In order to solve the problem of resource location failure in SALTE-U system, the resource location method under the condition of channel discontinuity and time uncertainty is studied. We propose the concepts of effective channel and effective frame number to eliminate the influence of channel time uncertainty. We design the generation method and update rule of the effective frame number, give the carrying position and analytical method of the effective frame number, and deduce the expression of resource location about the effective frame number. In order to ensure that the calculated time domain position of the resource always falls in the channel occupation period and the subframe category is always correct. The performance index and statistical formula of resource location are given, and the validity of the proposed scheme is verified. A new random access protocol and conflict control method are proposed to solve the problem that the random access protocol is not available under the condition of serious random access conflict and discontinuous channel in SALTE-U system. In order to improve system performance and channel utilization, we design a random access protocol based on effective channel and effective window length, which can avoid the difficulty to complete the interaction process and the long stay of users in the random access process due to the channel resource characteristics of the system. We propose a collision control method based on exponential attenuation of retransmission probability in order to mitigate the severe user conflicts caused by the excessive accumulation of users during the non-channel occupancy period and the simultaneous initiation of random access process during the channel occupancy period. Three performance indexes, namely, access rate, reselection rate and average delay, are defined to measure the performance of random access. The performance analysis is carried out and the expression of the above performance index is derived. Furthermore, the effectiveness of the proposed random access protocol and conflict control method is verified. Aiming at the contradiction between random access conflict resolution and uplink data transmission in SALTE-U system, the optimal random access channel (Random Access Channel,RACH) number allocation method is studied. With the constraints of random access success probability and average access delay, an optimization problem is proposed to maximize the number of shared uplink channels available for data transmission. A method for predicting the number of users based on joint arrival rate estimation and maximum likelihood estimation is proposed, and an analytical formula for the current number of users is obtained. An algorithm for finding the optimal number of RACH is proposed, which is used to solve the optimization problem to obtain the optimal number of RACH, so as to achieve the balance between the conflict resolution capability and the uplink data transmission capability.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.5

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