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首页> 外文期刊>IEEE Transactions on Information Theory >Optimal Power/Rate Allocation and Code Selection for Iterative Joint Detection of Coded Random CDMA
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Optimal Power/Rate Allocation and Code Selection for Iterative Joint Detection of Coded Random CDMA

机译：编码随机CDMA迭代联合检测的最优功率/速率分配和代码选择

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摘要

Iterative interference cancellation of coded code-division multiple access (CDMA) using random spreading with linear cancellation is analyzed. If users are grouped into power classes and Shannon bound approaching codes are used, a geometric power distribution achieves the additive white Gaussian noise (AWGN) channel Shannon bound as the numbers of classes becomes large. The optimal distribution of the size of these classes is shown to be uniform. If users are grouped into different rate classes with equal powers among equal rate users, the Shannon bound for AWGN channels can be achieved with an arbitrary distribution of the classes sizes, provided that the size of the largest rate class obeys the mild condition that its ratio of size to processing gain is much smaller than the inverse of the signal-to-noise ratio (SNR). The case of equal powers and equal rates among all users is addressed as a “worst case” scenario. It is argued that simple repetition codes provide for a larger achievable capacity than stronger codes. It is shown that this capacity monotonically increases as the rate of the code decreases. A density evolution analysis is used to show that the achievable rates exceed those of a minimum-mean square error filter applied to the uncoded signals. This lower bound is tight for small ratios of bit energy to noise power, and otherwise the iterative cancellation receiver provides an appreciably larger capacity. Relating to recent result from the application of statistical mechanics it is shown that the repetition-coded system with iterative cancellation achieves the performance of an equivalent optimal joint detector for uncoded transmission.
机译：分析了使用带有线性消除的随机扩展的编码码分多址（CDMA）的迭代干扰消除。如果将用户分组到功率类别中，并使用香农边界逼近代码，则随着功率类别的增加，几何功率分布会实现加性高斯白噪声（AWGN）信道香农边界。这些类别的大小的最佳分布显示为均匀。如果在等价用户中以相同的功率将用户分组到不同的等价级别中，则只要最大的等价级别的大小服从其比率的适度条件，就可以通过类大小的任意分布来实现AWGN信道的香农边界尺寸与处理增益之比远小于信噪比（SNR）的倒数。所有用户之间均等功率和均等费率的情况称为“最坏情况”。有人认为，简单的重复代码比强代码提供了更大的可实现容量。可以看出，随着编码率的降低，容量单调增加。密度演化分析用于显示可达到的速率超过应用于未编码信号的最小均方误差滤波器的速率。对于较低的位能量与噪声功率之比，此下限是严格的，否则迭代消除接收器将提供明显更大的容量。关于统计力学应用的最新结果，表明具有迭代抵消的重复编码系统达到了等效的最佳联合检测器的性能，适用于非编码传输。

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