TAILIEUCHUNG - Advanced wireless networks 4g technologies phần 4

Vì vậy, một kích thước, cụ thể là tần số, đã được thay thế bởi các tham số, hai sự chậm trễ. Đối với dự toán của hướng đến (DOA) trong mỗi chức năng chuyển giao hai chiều, ESPRIT dự toán và beamforming giả-nghịch đảo được sử dụng hφR (τi, XT) = A + HXR | EFFECTIVE LINK LAYER CAPACITY 243 Figure Shaping probability curves for nonsmooth mode. Rate cells ms Figure Shaping probability curves for smooth mode. EFFECTIVE LINK LAYER CAPACITY In the previous section we discussed the problem of effective characterization of the traffic source in terms of the parameters which are used to negotiate with the network a certain level of QoS. Similarly on the network side to enable the efficient support of quality of service QoS in 4G wireless networks it is essential to model a wireless channel in terms of connection-level QoS metoics such as data rate delay and delay-violation probability. The traditional wireless channel models channel models do not explicitly characterize a wireless channel in terms of these QoS metrics. In this section we discuss a link-layer channel model referred to as effective capacity EC 11 In this approach a wireles8 linkismodeledbytwo EC functions the probability of nonempty buffer and the QoS exponent of a connection. Then a simple and efficient algorithm to estimate these EC functions adYantagc of tOcEC link-layer modeling and estimation is ease 244 EFFECTIVE CAPACITY of translation into QoS guarantees such as delay bounds and hence efficiency in admission control and resource reservation. Conventional channel models discussed in Chapter 3 directly characterize the fluctuations in the amplitude of a radio signal. These models will be referred to as physical-layer channel models to distinguish them from the link-layer channel model discussed in this channel models provide aquick estimate of the physical-layer performance of wireless communications systems . symbol error rate vs SNR . However physical-layer channel models cannot be easily translated into complex link-layer QoS guarantees for a connection such as bounds on delay. The reason is that these complex QoS requirements need an analysis of the queueing behavior of the .

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