一种支持宽带无线多媒体网络QoS的动态呼叫接纳策略

Dynamic Call Admission Policy for Broadband Wireless Multimedia Networks

在无线网络中,小区微型化的趋势使得呼叫切换发生的频率越来越高,迫切需要一种有效的呼叫接纳控制策略,对有限的无线带宽资源进行分配,以保证切换时的QoS,同时使带宽利用率最高。传统的预留带宽策略(GC,guardchannel scheme)由于其固有的静态特征而不能适应流量模式的变化。最近,人们发现采用动态的随机控制策略能适应流量模式的变化,而且能使精度和稳定性大大提高。但将这种策略应用于多业务环境依然十分困难,挑战来自于多类呼叫的QoS要求、流量模式、切换率的多样性和宽带条件下的实时可计算性。在文[3]中,我们建立了一个随机控制模型,可以在宽带条件下实时地进行多业务接纳控制,但由于没有考虑复杂的边界条件,控制精度受到影响。本文,我们在考虑边界条件的情况下,求解该随机问题,并采用一种有效的数值方法,使计算复杂度大大降低,保证了计算的实时性。最后得到的多业务动态接纳控制策略具有较高的控制精度和良好的可计算性。仿真结果显示该策略能稳定地满足多业务QoS对呼叫中断概率的严格限制,同时又能保证信道的高利用率。

In wireless networks,bandwidth is extremely valuable resource. Therefore,an effective call admission con- trol is urgent for bandwidth allocation with the occurrence of handoff increasing. The traditional guard channel scheme (GC) and its numerous variants cannot adapt to changes in traffic pattern due to their static nature. Recently, the dynamic method using stochastic control is found to be preferred. But the dynamic control for multi-services is stil1 a problem. The main challenges with multiple types of traffic are that each has its own requirements' bandwidth, QoS guarantee,traffic characteristics and handoff rate. Moreover,the computational complexity is another challenge. In[3],we have set up a novel fictitious stochastic model to get dynamic call admission control. But this model has not considered the complex boundary conditions,so the control precision is not satisfied. In this paper, we consider the boundary conditions and its computation complexity for precision and real time control. As a result,we get an effec- tive multi-services dynamic call admission scheme to adapt for multiple types of sercvies in broadband wireless net- works. Numerical results of simulation show that our scheme steadily satisfies the hard constraint on call dropping probability of multi-services while maintaining a high channel throughput.