无线通信基础(双语)_教学课件_.pptVIP

1 j 1 2 i 1. Rule for determining the nearest cochannel neighbors i =1，j=2 2. Cochannel interference Frequency reuse needs to be structured so that cochannel interference is kept at an acceptable level. As the distance between cochannel cells increases, cochannel interference will decrease. If the cell size is fixed, the average signal-to-cochannel interference ratio will be independent of the transmitted power of each cell. The distance between the nearest cochannel cells in a hexagonal area can be calculated from the geometry R The distance between the centers of two adjacent hexagonal cells is The distance between the centers of two adjacent cochannel cells is D For hexagonal cells, there are six nearest cochannel neighbors to each cell Cochannel cells are located in tiers, and a candidate cell is surrounded by 6k cells in tier k The radius of the hexagon chaining the cochannel cells in the kth tier is given by kD Verify that the cell cluster size is N=i2+ij+j2, where i and j are the integer parameters determining the cochannel cells. 3.4.3 Direct-Sequence Spread Spectrum 3.4.4 Frequency-Hopped Spread Spectrum 3.4.5 Code Division Multiple Access With the limitation in spectral width, the maximum number of users (capacity) that can be supported in a wireless system is an important performance measure. In this chapter, the rationale behind cellular operation as a means of increasing system capacity is explained. 2、 Frequency reuse and mobility management 1、Introduction 3、 Cell cluster concept Usable spectral width Geographical coverage The high error rate has the effect of limiting the amount of throughput and rendering signal reception unreliable. Impairments in the propagation channel will result in a reduction of usable spectral width. Fiber 10-10 Wireless 10-2 ~10-3 System capacity can be interpreted as the largest number of users that can be supported. A larger population will mean a larger geographical coverage. City A single tra