tailieunhanh - Broadband Powerline Communications Networks Design phần 7

Pseudo-Bayesian thuật toán, dựa trên một phương pháp thiết lập giá trị ước tính của việc tồn đọng để ổn định các rãnh ALOHA giao thức, cũng được xem xét trong [FrigLe01, FrigLe01a, ZhuCo01], và tối thiểu Mean-Squared Lỗi thuật toán ước tính số lượng các trạm va chạm. | PLC MAC Layer 159 Pseudo-Bayesian Algorithm based on a method that establishes the estimated value of backlog in order to stabilize the slotted ALOHA protocols also considered in FrigLe01 FrigLe01a ZhuCo01 and Minimum Mean-Squared Error algorithm estimating the number of collided stations. To stabilize a slotted ALOHA protocol the task of the Pseudo-Bayesian Algorithm is to estimate number of backlog or network station n attempting to transmit new packets or retransmit collided packets. Then each packet will be transmitted with the probability P min 1 1 n . The minimum operation established an upper limit for the transmission probability and causes the access rate G np to become 1 Walke99 . A common problem of different stabilization algorithms is the calculation of an optimal retransmission probability because of dynamic load conditions in the network. Thus number of backlog n depends on the arrival rate as well as number of active stations in the network. If the calculation of an optimal transmission probability is carried out by a central instance for example base station there is an additional overhead information to be exchanged between network stations causing an extra signaling network load. Furthermore in communications networks operating under unfavorable disturbance conditions such as PLC signaling messages can be frequently destroyed which can also influence transmission of information necessary for calculation of the optimal retransmission probability between base and network stations. Finally despite complexity of such algorithms the result of their application is only a performance stabilization such as in the case of the dynamic backoff mechanism described above. To avoid the signaling exchange between base and network stations in Rivest s Pseudo-Bayesian algorithm every node estimates the number of backlog n and accordingly adjusts its transmission probability P 1 n ZhuCo01 . An update of the value n is carried out in accordance with the following .