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Mobile Wireless Communications using none todevelop none for asp.net web,windows application QR Code ISO speicification keying or on off ke none for none yed transmission (ASK or OOK). These simple digital modulation techniques are then extended to quadrature-amplitude modulation (QAM) techniques, with QPSK and 8-PSK, used in third-generation cellular systems, as special cases. A brief introduction to signal shaping in digital communications is included as well.

This material should be familiar to anyone with some background in digital communication systems. The further extension of these techniques to digital modulation techniques such as DPSK and GMSK used in wireless systems then follows quite readily and is easily described. The chapter concludes with an introduction to orthogonal frequency-division multiplexing (OFDM), including its implementation using Fast Fourier Transform techniques.

OFDM has been incorporated in high bit rate wireless LANs, described in 12. In 6 we describe the two major multiple access techniques, time-division multiple access (TDMA) and code-division multiple access (CDMA) used in digital wireless systems. TDMA systems incorporate a slotted repetitive frame structure, with individual users assigned one or more slots per frame.

This technique is quite similar to that used in modern digital (wired) telephone networks. The GSM and D-AMPS (IS-136) cellular systems are both examples of TDMA systems. CDMA systems, exempli ed by the second-generation IS-95 system and the third-generation cdma2000 and WCDMA systems, use pseudo-random coded transmission to provide user access to the cellular system.

All systems utilize FDMA access as well, with speci ed frequency assignments within an allocated spectral band further divided into time slots for TDMA transmission or used to carry multiple codes in the case of CDMA transmission. We provide rst an introductory discussion of TDMA. We then follow with an introduction to the basic elements of CDMA.

(This discussion of CDMA is deepened later in the book, speci cally in describing IS-95 in 8 and the third-generation CDMA systems in 10.) We follow this introduction to CDMA with some simple calculations of the system capacity potentially provided by CDMA. These calculations rely, in turn, on knowledge of the calculation of bit error probability.

For those readers not familiar with communication theory, we summarize classical results obtained for the detection of binary signals in noise, as well as the effect of fading on signal detectability. Error-probability improvement due to the use of diversity techniques discussed in 2 is described brie y as well. These calculations of CDMA capacity using simple, analytical models enable us to compare, in concluding the chapter, the system-capacity performance of TDMA and CDMA systems.

We do stress that the capacity results obtained assume idealized models of cellular systems, and may differ considerably in the real-world environment. The use of system models in this chapter and others following do serve, however, to focus attention on the most important parameters and design choices in the deployment of wireless systems. 7, on coding for error detection and correction, completes the discussion of introductory material designed to provide the reader with the background necessary to understand both the operation and performance of digital wireless systems.

Much of this chapter involves material often studied in introductory courses on communication systems and theory. A user with prior knowledge of coding theory could therefore use the discussion in this chapter for review, while focusing on the examples provided of the application of these coding techniques to the third-generation cellular systems discussed later in 10. We begin the discussion with an introduction to block coding for error correction and detection.

We focus speci cally on so-called cyclic codes used commonly in. Introduction and overview wireless systems. T none for none he section on block coding is followed by a discussion of convolutional coding, with emphasis on the Viterbi algorithm and performance improvements possibly due to the use of convolutional coding. We conclude 7 with a brief discussion of turbo coding adopted for use with third-generation CDMA cellular systems.

8 begins the detailed discussion of speci c digital wireless systems described in this book. This chapter focuses on GSM, D-AMPS or IS-136, and IS-95, the three second-generation cellular systems already mentioned a number of times in our discussion above. For each of these systems, we describe the various control signals transmitted in both directions across the air interface between mobile and base station required to register a mobile and set up a call.

Control signals and traf c signals carrying the desired information are sent over channels de ned for each of these categories. The control signals include, among others, synchronization signals, paging signals asking a particular mobile to respond to an incoming call, and access signals, used by a mobile to request a traf c channel for the transmission of information, and by the base station to respond to the request. For the TDMA-based GSM and IS-136 systems, the various channels de ned correspond to speci ed bit sequences within the time slots occurring in each frame.

We describe for each of these systems the repetitive frame structure, as well as the bit allocations within each time slot comprising a frame. We describe as well the various messages transmitted for each of the control channel categories, focusing on the procedure required to set up a call. For the CDMA-based IS-95, these various channels correspond to speci ed codes.

We begin the discussion of IS-95 by providing block-diagram descriptions of the traf c channel portion of the system used to transmit the actual call information. We then move on to the control channels of the system, used by the mobile to obtain necessary timing information from the base station, to respond to pages, and to request access to the system. This discussion of the various code-based channels and block diagrams of the system sub-structure used to implement them, serves to deepen the discussion of CDMA systems begun in 6, as noted earlier.

One thus gains more familiarity with the concepts of CDMA by studying the speci c system IS-95. This knowledge of the basic aspects of CDMA will be further strengthened in 10, in discussing third-generation systems, again as noted above. Once the various IS-95 channel block diagrams are discussed, we show how the various channels are used by a mobile to acquire necessary phase and timing information, to register with the base station, and then to set up a call, paralleling the earlier discussion of setting up a call in the TDMA case.

The formats of the various messages carried over the different channels are described as well. The discussion thus far of the material in 8 has focused on signals carried across the air or radio interface between mobile station and base station. Much of the material in the earlier chapters implicitly focuses on the radio portion of wireless systems as well, but the expected mobility of users in these systems leads to necessary signaling through the wired networks to which the wireless systems are generally connected.

We have already alluded implicitly to this possibility by mentioning earlier the need to control handoffs occurring when mobile stations cross cell boundaries. Mobile management plays a critical role in the operation of wireless cellular systems, not only for the proper control of handoffs, but for the location of mobiles when they roam, and for the appropriate paging of mobiles within a given cell, once they are located. These three aspects of mobile.

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