Praise for Fundamentals of WiMAX

C H A P T E R 1 1Link-Level Performanceof WiMAXThe goal of any communication system is to reliably deliver information bits from the transmitterto the receiver, using a given amount of spectrum and power. Since both spectrumand power are precious resources in a wireless network, it should come as no surprise that efficiencyis determined by the maximum rate at which information can be delivered using the leastamount of spectrum and power. Since each information bit must reach the intended receiver witha certain amount of energy—over the noise level—a network’s power efficiency and bandwidthefficiency cannot be maximized at the same time; there must be a trade-off between them. Thus,based on the nature of the intended application, each wireless network chooses an appropriatetrade-off between bandwidth efficiency and power efficiency. Wireless networks intended forlow-data-rate applications are usually designed to be more power efficient, whereas wireless networksintended for high-data-rate applications are usually designed to be more bandwidth efficient.Most current wireless standards, including WiMAX (IEEE 802.16e-2005), provide a widerange of modulation and coding techniques that allow the system to continuously adapt frombeing power efficient to bandwidth efficient, depending on the nature of the application. Theamount of available spectrum for licensed operation is usually constrained by the allocationsprovided by the regulatory authority. Thus, in the given spectrum allocation, most cellular communicationsystems strive to maximize capacity while using the minimum amount of power.Due to the complex and nonlinear nature of most wireless systems and channels, it is virtuallyimpossible to determine the exact performance and capacity of a wireless network, based on analyticalmethods. Analytical methods can often be used to derive bounds on the system capacity inchannels with well-defined statistical properties, such as flat-fading Rayleigh channels or AWGNchannels. Computer simulations, on the other hand, not only provide more accurate results but canalso model more complex channels and incorporate the effects of implementation imperfections,such as performance degradation owing to channel estimation and tracking errors [19].365