Spatially Multiplexed CDMA Multiuser Underwater Acoustic Communications
Spatially Multiplexed CDMA Multiuser Underwater Acoustic Communications
复制标题
DOI：
10.1109/joe.2015.2412993
复制
发表时间：
2016-01-01
影响因子：
4.1
通讯作者：
Yang, T. C.
中科院分区：
文献类型：
--
作者：
Yang, T. C.
直接序列（DS）码分多址（CDMA）信令允许多个用户以降低速率为代价在相同带宽上同时通信。由于在多径丰富的水下信道中存在严重的共信道干扰（CoI），因此仅演示了不超过4个用户。多输入多输出（MIMO）通信也允许多个用户。使用并行/顺序干扰消除方案，实验结果显示了类似的用户数量限制。为了将用户数量扩展到4个以上（某些应用需要），建议将CDMA与MIMO结合起来，利用无源相位共轭的时空处理增益和扩展码的近似正交性来去除（增加的）CoI。接收机算法使用简单的匹配滤波器，没有显式的信道均衡和CoI抵消。利用基于实验测量的信道脉冲响应的模拟数据，研究了算法性能作为输入信噪比的函数。m序列使用127、255和511个芯片。一个发现，对于所研究的通道，通常需要255/511芯片支持8个用户，需要127/255芯片支持6个用户。多用户通信演示了8个用户的海上数据，扩展码为511个芯片，产生零误码。数据速率类似于8比特/秒/用户，给定4 kHz带宽。
Direct-sequence (DS) code-division-multiple-access (CDMA) signaling allows multiple users to communicate simultaneously over the same bandwidth at the expense of a reduced rate. Due to severe cochannel interference (CoI) in multipath rich underwater channels, no more than 4 users have been demonstrated. Multiple-input-multiple-output (MIMO) communication also allows multiple users. Using parallel/sequential interference cancellation schemes, experimental results show similar limitations on the number of users. To extend the number of users beyond four (as required for certain applications), it is proposed to combine CDMA with MIMO, utilizing the spatial-temporal processing gain of passive-phase conjugation, and the approximate-orthogonality of the spreading codes to remove the (increased) CoI. The receiver algorithm uses simple matched filters without explicit channel-equalization and CoI cancellation. The algorithm performance is studied as a function of input-SNR, using simulated data based on experimentally measured channel impulse responses. M-sequences with 127, 255 and 511 chips are used. One finds that 255/511 chips are generally required to support 8 users, and 127/255 chips are needed to support 6 users for the channel studied. Multiuser communications are demonstrated with at-sea data for 8 users, with spreading codes of 511 chips, yielding zero bit errors. The data rate is similar to 8 bits/s/user, given 4 kHz bandwidth.