**1. Introduction**

Broadband Wireless Access (BWA) has emerged as a promising solution for last mile access technology to provide high speed internet access in the residential as well as small and medium sized enterprise sectors. At this moment, cable and DSL technologies are providing broadband service in these sectors. But the practical difficulties in deployment have prevented them from reaching many potential broadband internet customers. Many areas throughout the world currently are not under broadband access facilities. Even many urban and suburban locations may not be served by DSL connectivity as it can only reach about three miles from the central office switch [1]. On the other side many older cable networks do not have return channel which will prevent to offer internet access and many commercial areas are often not covered by cable network. But with BWA this difficulties can be overcomed. Because of its wireless nature, it can be faster to deploy, easier to scale and more flexible, thereby giving it the potential to serve customers not served or not satisfied by their wired broadband alternatives.

IEEE 802.16 standard for BWA and its associated industry consortium, Worldwide Interoper‐ ability for Microwave Access (WiMAX) forum promise to offer high data rate over large areas to a large number of users where broadband is unavailable. This is the first industry wide standard that can be used for fixed wireless access with substantially higher bandwidth than most cellular networks [2]. Wireless broadband systems have been in use for many years, but the development of this standard enables economy of scale that can bring down the cost of equipment, ensure interoperability, and reduce investment risk for operators.

The first version of the IEEE 802.16 standard operates in the 10–66GHz frequency band and requires line of sight (LOS) towers. Later the standard extended its operation through different PHY specification to 2-11 GHz frequency band enabling non line of sight (NLOS) connections, which require techniques that efficiently mitigate the impairment of fading and multipath [3]. Taking the advantage of OFDM technique the PHY is able to provide robust broadband service

© 2013 Shokair and Sakran; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

in hostile wireless channel. The OFDM based physical layer of the IEEE 802.16 standard has been standardized in close cooperation with the European Telecommunications Standards Institute (ETSI) High PERformance Metropolitan Area Network (HiperMAN) [4]. Thus, the HiperMAN standard and the OFDM based physical layer of IEEE 802.16 are nearly identical. Both OFDM based physical layers shall comply with each other and a global OFDM system should emerge [5]. The WiMAX forum certified products for BWA comply with the both standards.

Some researchers investigate the effect of nonlinear amplifier in WiMAX [6] and apply Clipping as a simple method [7], CORDIC Algorithm [8], and Tone Reservation [9] to reduce PAPR in WiMAX system.

In this chapter, proposed WiMAX system will be studied. This system will be compared with the conventional system. Where the companding technique is used to reduce PAPR based on the properties of the µ-law that uses for decreasing dynamics range of the signal. Moreover, the performance of the proposed system will be compared with the system that uses clipping as a reduction of PAPR. These systems will be investigated under SUI channels and AWGN.

In Section 1.2, the broadband channel will be explained. In section 1.3 SUI multipath Channel Models will be investigated. The performance of MMSE equalizer over SUI model will be study in section 1.4. In section 1.5, a system model of WiMAX for PAPR will be explained. PAPR Reduction Technique Using µ-Law Compander is studied in Section 1.6. Finally, summary will be made.

classified as either *statistical* or *empirical*. Statistical models are simpler and are useful for analysis and simulations. Empirical models are more complicated but usually represent a specific type of channel more accurately. There are several channels models which are

**Figure 1.** A channel with a few major paths of different lengths, with the receiver seeing a number of locally scattered

PAPR Reduction in WiMAX System http://dx.doi.org/10.5772/55380 37

As we have noted, the received signal in a wireless system is the superposition of numerous reflections, or multipath components. The reflections may arrive very closely spaced in time — for example, if there is local scattering around the receiver—or at relatively longer intervals.

Figure 2 shows that when the reflections arrive at nearly the same time, constructive and destructive interference between the reflections causes the envelope of the aggregate received

In this section, we summarize statistical methods for characterizing the amplitude and power

Suppose that the number of scatters is large and that the angles of arrival between them are uncorrelated. From the Central Limit Theorem, it can be shown that the in-phase (cosine) and quadrature (sine) components of *r*(t), denoted as *rI* (*t*) and *rQ*(*t*), follow two independent time

Consider a snapshot value of at time *t* =0, and note that *r*(0)= *rI* (0) +*rQ*(0). Since the values *rI* (0) and *rQ*(0) are Gaussian random variables, it can be shown that the distribution of the envelope

of *r*(t) when all the reflections arrive approximately at the same time.

explained in the following,

versions of those paths.

**2.1. Statistical channel models**

signal *r*(t) to vary substantially.

correlated Gaussian random processes.

*2.1.1. Rayleigh fading*
