OFDM系统中的资源调度

Dynamic Resource Management in OFDM Wireless Systems

资源调度可以显著地改善通信系统的频谱效率和吞吐量。文中给出了OFDM下行链路中3种不同的时隙调度策略,这些策略都是以CDMA/HDR中比例公平算法(ProportionalFair)为基础。比较和分析了3种子带分配的方案。首先将OFDM的子载波划分为若干个子带,目的是减少系统的反馈量。所有的用户同时竞争所有的子带。仿真表明,子带的划分以16～32个比较合适,而调度可以将系统的吞吐量提高0.4～1倍,调度方案3实现了性能和复杂度的折衷,是一种好的选择。

The authors consider the problem of fair scheduling in the downlink of Orthogonal Frequency Division (OFDM) systems. Based on the proportional fair scheduling algorithm proposed in the CDMA/HDR,the authors present three schemes to manage the parallel subcarriers in the OFDM system to utilize the time selectivity and frequency selectivity. Subcarriers in a slot are divided into several nonoverlapped subbands, which are the scheduling objects. The first scheme is that every subband is placed a scheduler and the average rates are updated independently; the second scheme is that transfer the two-dimensional channel resource into one-dimension equivalent channel, and then schedule the resource like in HDR systems; the third one is that users contend every subband in a same slot using one scheduler without updating the average rates, after finishing a slot, the average rates are updated together. Compared to the first scheme, the third one has the least complexity and its performance degrades little. It is shown that system throughput is improved by 40%～100%, the appropriate number of subbands is 16～32 and scheme 3 is an appropriate choice for practice systems.