Bảo hiểm cho các hệ thống LMDS liên quan đến các tế bào nhỏ hơn bán kính km đến 5 và yêu cầu lặp được đặt trong một cấu hình Line Of Sight (LOS). Phạm vi bảo hiểm địa phương với một băng thông có sẵn lớn làm cho LMDS hệ thống phù hợp | PERFORMANCE MEASURES 67 Slotted ALOHA was selected as the random access protocol in the RA channel. The BEB algorithm was used to provide stability to the protocol. Such schemes reduce access delay by reducing consecutive collision in the RA channel. In addition the multipleRA mode provides an additional layer of control for reducing collisions. In situations in which the random access protocol is unable to produce a successful request the adaptive channel access strategy coupled with the BEB algorithm significantly reduces the collision probability in the request channel. We summarize the relevant features of ARCMA protocol. Efficient channel utilization Schemes such as the adaptive RA channel the special handling of CBR traffic and the piggyback strategy significantly improve channel utilization. Slot-by-slot transmission MS receives ACK to transmit request almost immediately on a slot-by-slot basis. When collision occurs MSs are quickly aware of their failed request and may retransmit in the next time slot. For a protocol that transmits on a frame-by-frame by periods basis the requesting MS has to wait until the next frame before receiving any acknowledgment. A frame usually has the length in bits of multiple time slots. This causes delay that can be critical in a delay-sensitive service. In addition there can be empty slots within that frame that could have been used for retransmission. Transparency to AAL To reduce the integration complexity between wired and wireless networks a protocol must provide seamless inter-networking such that the ATM Adaptation-Layer AAL is not involved. ARCMA protocol is essentially self-contained within its own network layer. The strategy does not involve the AAL. Small RA packet In ARCMA implementation we use a single byte 256 mobiles request in the RA slot. Therefore the RA slot is just a fraction of an ATM packet 53 bytes . Collision in the RA channel only wastes a small amount of the scarce wireless spectrum. Preserved packet .
