Design Trade-offs in Cellula rIPCS Systems
On-Ching Yue · 1996
With the increasing demand for all kinds of wireless access services, including cellular/PCS, wireless local loop, and broadband access, the system architects will have opportunities to design new communication systems, not necessarily based on existing wireless standards, such as 15-54/136, GSM, IS-95, CT-2, and DCS 1800. In the design of wireless communication systems, there are usually multiple objectives such as low cost, small size, high reliability, and large capacity The system architect would need to study trade-offs among different combmations of modulatton, coding, multiple access, and antenna techniques to determine the best design In this tutorial we focus on the trade-offs between user bandwidth and multi-user interference in order to maximize system capacity. The design trade-offs are depicted on a B - yo plane, where B is the user bandwidth and yo is the carrier-to-interference ratio (Cl) For FflDMA and CDMA systems, the author first shows that the contours of equal system capacity are slraight lines with different slopes depending on the propagation environment, and the capacity decreases for increasing 5 and yo Then as feasible solutions, the author plots the different combinations of modulation and coding with diversity to satisfy a certain quality of service in a multipath fading environment The best design is obtained by moving a line with a certain slope from the lower left corner in the B - yo plane until it touches the first feasible solution From these plots we can see that, for example, while 1/2-rate channel coding is the best choice for F/TDMA systems, 1/3-rate 15 better for CDMA systems As the application scenario changes, different combinations of communication techniques would emerge as optimal choices.