Study on Spread Spectrum Packet Communications

讨论了一种采用统一扩频码的扩频ALOHA系统的性能、设计和传输效率。对系统进行了概述，并通过理论分析和近似方法推导了两种情况下的误码性能。与计算机模拟结果的比较表明，理论结果与模拟结果吻合较好，在低E_b/N_0范围内，近似结果与模拟结果吻合较好。设计了一种以符号时序恢复和载波恢复为重点的解调器。建议提供一个简短的序言，以便对这些恢复应用同步循环添加。通过对符号时序检测和载波偏移估计的性能评估，表明该方案显著提高了系统的性能。推导了三种不同情况下的扩散ALOHA系统的传输效率。将第一种情况下的传输效率与传统开槽ALOHA系统在相同频带下的传输效率进行了定量比较，得出了与开槽ALOHA系统相比，扩展ALOHA系统具有较好的传输性能，且发射功率较低。对于另外两种情况，将使用统一扩频码的系统与使用不同扩频码的系统进行传输效率的比较，可以明显看出，在较长的分组长度下，使用统一扩频码的系统比使用不同扩频码的系统具有更好的传输性能。最后提出了利用啁啾信号实现扩张式aloha系统。首先从理论上描述了使用啁啾匹配滤波器的相关过程，并澄清了在接收端进行的信号处理，特别关注了块解调器。讨论了计算机仿真得到的误码率性能在各种条件下的定量评价。少

A spread ALOHA system using a unified spread spectrum code is discussed in terms of its performance, design and transmission efficiency. The system is outlined and then the bit error performance under two conditions is derived by a theoretical analysis and an approximate method. The comparison it with the results obtained by means of computer simulation indicates that the theoretical results coincide perfectly with the simulated ones and that the approximayte results coincide with the simulated results in the low E_b/N_0 range. A demondulator is designed focussing on symbol timing recovery and carrier recovery. It is proposed that the provision of a short preamble enables to apply a synchronous cyclic addition to these recoveries. It is concluded as a result of performance evaluation concerming symbol timing detection and carrier offset estimation that the proposed scheme improves the performance remarkably. The transmission efficiency obtained in the spread ALOHA system is derived for … More three cases. Comparing quantitatively the transmission efficiency in the first case with that of the conventional slotted ALOHA system under the condition at the same frequency bandwidth, it is concluded that the spread ALOHA system gives a good performance with the lower transmitting power compared with that of the slotted ALOHA system. As for the other two cases, the system using a unified spread spectrum code is compared with that using different spread spectrum codes in terms of transmission efficiency and it becomes obvious that the former system provides better performance for the long packet length than the latter one. Finally it is proposed to realize a spread-ALOHA system by using a chirp signal. Correlation process using the chirp matched filter is theoretically described at first and signal processings to be performed in the receiving side are clarified, in particular focussing on the block demodulator. The quantitative evaluation under various conditions is discussed concerning bit error rate performance obtained by means of computer simulation. Less