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mcgraw hill wireless data demystified phần 10

này được gọi là giờ cấu hình lại một phần cho các trường hợp như vậy. 6. RMM sẽ làm cho một con trỏ tham chiếu (bản sao) của đối tượng trong chuỗi bóng tối (* BPC_id) BPC. Sau đó nó sẽ đưa BPC_id * ở trong trạng thái lơ lửng: | Chapter 23 Summary Recommendations and Conclusions 509 demonstrated to provide reliable wireless data rates exceeding 100 Mbps within buildings with extremely low power spectral densities. Another exciting development particularly applicable to home or campus wireless data distribution is the commercialization of orthogonal frequency-division multiplexing OFDM . OFDM offers multiple access and signal processing benefits that have not been available in previous modulation methods. It allows wireless data networks to pack high spectral efficiency into relatively small spectrum bandwidths. This is similar to how digital subscriber line DSL technology allows high wireless data rates to be passed through low-bandwidth copper cables. IEEE 802.16 point-to-multipoint MAN wireless data networks certainly could provide tetherless broadband access in the local loop and are already doing so in developing nations. New discoveries in the 1990s have shown us how to exploit the spatial dimension of wireless data channels through the use of multiple antennas at the transmitter and receiver where significant gains in either energy efficiency or more important perhaps spectral efficiency can be obtained. Pioneering work showed that the theoretical wireless data rates obtained with such systems in an independent Rayleigh scattering environment increase linearly with the number of antennas and these rates approach 90 percent of the theoretical maximum Shannon capacity. New space-time methods have been shown to offer more than an order of magnitude of increase in spectral efficiency over today s modulation and coding techniques used in current WLANs and cell phone systems and these methods hold promise for wireless data networks of the future. As an example Lucent s V-BLAST laboratory prototype system was demonstrated to provide spectral efficiencies of 20 to 40 bps Hz at average signal-to-noise ratio ranging from 24 to 34 dB in an indoor environment and potential capacities on the .