Orthogonal frequency-division multiplexing with random multiple access (OFDRMA) is discussed for down-link communications, whereby a single base-station transmits information towards several active users. Current methods for down-link communication partition the frequency resources among the active users in an orthogonal fashion, i.e. a central unit (typically the base-station itself) dynamically allocates the resources such that each user is allocated a fixed and exclusive set of sub-bands (a.k.a. bins, or subcarriers). The task and overhead required for orchestrating the frequency sub-bands allocations among the users in an optimal fashion can be quite cumbersome, and typically involves increased computational complexity, latency and bandwidth resources. The main purpose we address in this paper is to avoid the task and overhead required in the state-of-the-art OFDM systems in both the base-station and the users, while sacrificing as little as possible in terms of users side error rate performance. This is of particular importance in multi-user multiple-input multiple-output systems, which become increasingly popular these recent years. In OFDRMA a user is assumed to be allocated with a predetermined, randomly selected frequency bins. A multi-antenna multi-user delivery approach is presented based on pre-coding and multi-cast transmission. It is shown to provide robustness against the forced randomness of the scheme. Simulation results are provided for demonstrating the performance attainable with OFDRMA and the proposed transmission scheme.

讨论了用于下行链路通信的具有随机多址的正交频分复用（OFDRMA），其中单个基站向多个活动用户发送信息。当前用于下行链路通信的方法以正交方式在活动用户之间分配频率资源，即中央单元（通常是基站本身）动态分配资源，以便为每个用户分配固定的排他子集。频段（又称垃圾箱或副载波）。以最佳方式在用户之间协调频率子带分配所需的任务和开销可能非常繁琐，并且通常涉及增加的计算复杂性，等待时间和带宽资源。我们在本文中解决的主要目的是避免在基站和用户中使用最新的OFDM系统所需的任务和开销，同时尽可能减少用户侧错误率性能。这在最近几年变得越来越流行的多用户多输入多输出系统中尤其重要。在OFDRMA中，假定为用户分配了预定的，随机选择的频点。提出了一种基于预编码和多播传输的多天线多用户传递方法。它显示出对方案的强制随机性具有鲁棒性。仿真结果提供了演示用OFDRMA和所提出的传输方案可达到的性能。