[...]... Orthogonal CDMA GENERALIZED CDMA 5 Gd(f) Gss(f) − 1 Tc − 1 Td 0 1 Td 1 Tc Data Bw Spread Bandwidth Figure 1.4 The power spectrum of data and spread signal orthogonal or synchronous CDMA In the second case, spreading is achieved with Pseudo-random Noise (PN) sequences Then we have the conventional asynchronous CDMA, also called direct sequence CDMA (DS /CDMA) The Orthogonal CDMA Orthogonal CDMA (O -CDMA) ... PN-sequence (wi ∈ {+1, −1}), with L N 14 1.3.1 CDMA: ACCESS AND SWITCHING Spread-Spectrum In this section, as in that for the Spread-Spectrum (SS) CDMA with real encoding sequences, we examine the orthogonal and pseudo-orthogonal SS -CDMA, but with complex sequences Here, we also derive the conventional Frequency Division Multiple Access (FDMA) and the frequency hopping CDMA as special cases of a more general... For example, accessing users may form groups on the basis of common services or location A two-step process may then be used for the access of users as individuals and as groups Here we present two applications: the first is a two-step access for wireless networks; and the second is a method of multiplexing multiple symbol rates A: Two-Step Access Method In this application a composite access method... distributed 18 CDMA: ACCESS AND SWITCHING over all bins, thus providing diversity in frequency selective fading channels On the other hand, FDMA does not require power control We also assume that all received signals are synchronized in both time and phase Therefore, this type of FDMA is a synchronous one and it does not require a ‘guard-band’ between the frequency bins If we assume asynchronous complex CDMA. .. conditions In addition we have presented composite multiple access methods such as spread-spectrum and time multiple access (SS&TMA) using the method of extended sequences given in Chapter 2 We have also presented applications of composite access methods for wireless two-step access networks, and for multiplexing multiple symbol rates in orthogonal CDMA channels ... pulse-shape, for example, may be time-limited or bandwidth-limited : Data Symbol Encoder User Encoder User Decoder Symbol Decoder : User Code Figure 1.1 SYNC User Code The multiuser data communications process Data GENERALIZED CDMA 3 G -CDMA G-FDMA DS -CDMA FDMA FH -CDMA G-TDMA TDMA Figure 1.2 G-PDMA The G -CDMA as the super-set of the multiple access methods Each set of parameters (1), (2) and (3) defines... accessing users in different satellite beams A similar process can be employed for the case of time overspreading The concept of spreading in spectrum and time (called spread-spectrum and time multiple access) is examined in the section that follows 1.4.1 Spread-Spectrum and Time Multiple Access Let us consider the real (binary) orthogonal code matrices a and b with sizes Na and Nb , respectively Also,... Assuming that the user of interest m = 0 has its receiver and transmitter synchronized ( ) at τ0 = 0 and φ0 = 0 for all , we may recover its data as shown below: M −1 rI (t) cos[2πfc ( + 1/2)t] = c0 /2 + cm m=1 where the vectors c0 and cm are defined as c0 = [a0 c0, (t)] for cm = [am cosφ( ) m cm, (t − τm )] for 0 ≤ ≤ N/2 − 1 and 0 ≤ ≤ N/2 − 1 and m = 1, 2, , M − 1 cm (t) = cm g(t), (cm = ±1) The data... extended codes is also an orthogonal access As examples of composite multiple access we may consider the following: (1) spectrum overspreading; (2) time overspreading; and (3) spectrum and time spreading using real or complex sequences in each step of spreading Spectrum overspreading is formed by spreading and overspreading in the spectrum for the purpose of providing access to individual users as well... = 0 and di,0 = 1 Then, V ar{Zi } = = P 4Td P 4Td M τ 2 2 [Rj,i (τ ) + Rj,i (τ )]dτ j=1 0 M N −1 j=1 l=0 (l+1)Tc 2 2 [Rj,i (τ ) + Rj,i (τ )]dτ lTc for 0 ≤ lTc ≤ τ ≤ (l+1)Tc ≤ Td The expected values have been computed with respect to the mutually independent random variables φj , τj , dj,−1 and dj,0 for 1 ≤ j ≤ M and j = i We have assumed that φj is uniformly distributed on the interval [0, π] and τj . y0 w0 h1" alt="" CDMA: Access and Switching For Terrestrial and Satellite Networks Diakoumis Gerakoulis AT&T Labs-Research, USA Evaggelos Geraniotis University of Maryland, USA JOHN WILEY. Data Gerakoulis, Diakoumis P. CDMA: access and switching for terrestrial and satellite networks/ Diakoumis Gerakoulis, Evaggelos Geraniotis. p.cm. Includes bibliographical references and index. ISBN 0-471-49184-5. 83 4.2 SwitchedCDMA(SW /CDMA) Architectures 84 4.2.1 Satellite Switched CDMA (SS /CDMA) System 84 4.2.2 SW/CDMAApplicationsinTerrestrialNetworks 88 4.3 PerformanceEvaluationofCodeDivisionSwitching 93 4.3.1