High-Density Random Access for High-Speed Satellite Data Services

近年来，人们对卫星通信的兴趣又有了强烈的复苏。例如，欧洲航天局（欧空局）正在研究利用多点、高容量地球静止卫星的卫星无线数据服务。这种系统将需要每秒百万兆字节数量级的卫星吞吐能力，以便在经济上与地面无线服务竞争。 现代卫星采用多点波束，能够覆盖很大的地理区域，为大量用户提供服务。当通过卫星的流量增加到基本访问和通信方法不再足以满足数据需求时，就会出现困难。上行链路上的传输和下行链路上的应答接收之间的长往返延迟使这一困难更加复杂，这妨碍了发射机之间的快速协调。接收机还需要能够解决信号冲突，并且能够估计和跟踪多个用户终端的信道条件。这些挑战是拟议研究项目的主要重点。 随机接入竞争解决的最新变化在整个传输帧中在随机分布的时隙中发送数据分组的多个副本。该方法在统计上增加了分组冲突的速率，但是增加了分组的至少一个副本被无冲突地接收的概率。然后，可以从也发送该分组的其他时隙中消除该分组，从而允许对整个帧进行迭代剥离解码。理论研究表明，这种方法可以实现80%的单用户容量的实际情况下，这代表了一个巨大的改进，37%的基本时隙ALOHA协议实现。 然而，该信道本身是多址信道，因此它具有上级任何复用信道的理论容量。利用这一优势需要结合联合检测原则。多分组接收（MPR）将解决迭代干扰消除，最近已被证明能够接近多址信道容量在理论上。然而，在可以部署这样的MPR接收器之前仍然存在实质性的问题。该项目的重点是现实的信道传播模型时出现的挑战，特别是具有高度动态行为的信道。预计这项工作的基本结果将导致频谱资源的利用率提高和网络的鲁棒性。我们一直在与德国航空航天研究所（DLR）合作，这笔赠款将加速这一合作，并导致达尔豪西大学在资源有效的数据通信方面的强大研究计划。

In recent years there has been a strong resurgence in interest in satellite communications. The European Space Agency (ESA), for example is investigating satellite-based wireless data services using multi-spot, high-capacity geo-stationary satellites. Such a system will require a satellite throughput capacity on the order of a terabyte/s in order to be economically competitive with ground-based wireless services.  A modern satellite, operating with multiple spot beams, is capable of covering a large geographic area and servicing a very large number of users. Difficulties arise when the traffic through the satellite increases to the point where basic access and communications methods no longer suffice to service the data demand. This difficulty is compounded by the long round-trip delays between transmissions on the up-link and reception of acknowledgements on the down-link, which prevents rapid coordination between transmitters. The receiver also needs to be able to resolve signal collisions and be able to estimate and track channel conditions for a multitude of user terminals. These challenges represent a are the major focus of the proposed research project. The most recent variations of random access contention resolution transmit multiple copies of a data packet in randomly distributed time slots throughout a transmission frame. This approach statistically increases the rate of packet collisions, but the probability that at least one copy of a packet is received collision-free is increased. This packet can then be cancelled from the other time slots where it was also transmitted, allowing for iterative peel-off decoding of the entire frame. Theoretical studies have shown that this method can achieve 80% of the single user capacity for practical scenarios, which represents a vast improvement over the 37% achievable with a basic slotted ALOHA protocol.  However, the channel itself, is a multiple access channel, and as such it has a theoretical capacity which is superior to that of any multiplexed channel. Exploitation of this advantage requires the incorporation of joint detection principles. Multi-packet reception(MPR) will be addressed with iterative interference cancellation, which has recently been shown to be able to approach the multiple access channel capacity in theory. However, substantial problems remain before such MPR receivers can be deployed. This project focuses on the challenges that arise when realistic channel propagation models are used, in particular channels with highly dynamic behavior. It is anticipated that the fundamental results from this work will lead to increased utilization of spectral resources and robustness of networks. We have been collaborating with the German Aerospace Institute (DLR), and this grant will accelerate this collaboration, and lead to a strong research program in resource-efficient data communications at Dalhousie University.