Capacity Estimation in Multiple-Chip-Rate DS/CDMA Systems Supporting Multimedia Services

Transcription

1 Wireless Personal Communications 4: 29 47, Kluwer Academic Publishers Printed in the Netherlands Capacity Estimation in Multiple-Chip-Rate DS/CDMA Systems Supporting Multimedia Services YOUNG WOO KIM, SEUNG JOON LEE, JEONG HO KIM, YOUNG HOON KWON and DAN KEUN SUNG Department of Electrical Engineering, Korea Advance Institute of Science and Technology, 373- Kusong-dong, Yusong-gu, Taejon , Korea or Abstract This paper is concerned with capacity estimation in multiple-chip-rate (MCR) DS/CDMA systems supporting multimedia services with different information rates and quality requirements Considering both power spectral density (PSD) over a radio frequency (RF) band and the effect of RF input filtering on the receiver, capacity that satisfies the requirement of the bit energy-to-interference PSD ratio is derived The optimum value of the received power which causes the least interference for other users while maintaining an acceptable quality-of-service (QoS) requirement is also derived The results show that system performance is strongly affected by a selected channel assignment strategy Therefore, it is critical to efficiently assign radio resources in MCR-DS/CDMA systems that support high capacity and a low blocking rate Keywords: multiple-chip-rate DS/CDMA, capacity estimation, optimum received power Introduction Third-generation wireless systems, such as the IMT-2000 and the UMTS, are required to accommodate a wide variety of services, including high quality voice, data, facsimile, video, and interactive applications, with information bit rates ranging from a few kb/s to 2 Mb/s [] Code division multiple access (CDMA) is a promising technique that complies with the above requirements Direct sequence (DS)-CDMA is attractive because of its flexibility in supporting multimedia traffic, as well as low interference coexistence with other CDMA or narrow-band systems operating in the same frequency band [2] Two approaches for accommodating multi-rate services in DS-CDMA systems have been proposed One is to use either a single-code or a multi-code DS-CDMA system in a single RF channel bandwidth [3] The other is to use an MCR-DS/CDMA system in multiple RF channel bandwidths [, 5, 6, 7] The frequency bandwidth of an MCR-DS/CDMA system is selected according to the maximum information rate to be supported MCR-DS/CDMA systems were proposed by the Code Division Testbed (CODIT) project [, 5], OKI [6], and ETRI [7] In the experimental CODIT testbed, an MCR-DS/CDMA system was proposed with three different chip rates corresponding to three different RF channel bandwidths of approximately, 5, and 20 MHz The three RF channel bandwidths of this system are referred to as narrow-band, medium-band, and wide-band RF channels In this system, low-rate services (eg, voice) can be optionally accommodated on narrow-band or on medium-band channels The MHz channel can be allocated as a standard RF channel for low-rate voice mobile phones, and 5 MHz This study was supported in part by the Korea Science and Engineering Foundation

2 30 Young Woo Kim et al can be used as an option for providing a higher grade-of-service (GoS) High-rate services (64 kb/s and above) require RF channels of 5 or 20 MHz For flexible use of limited RF resources, MCR-DS/CDMA systems are preferable to single RF channel bandwidth systems [5] However, due to the complexity of obtaining quantitative results on the performance of MCR-DS/CDMA systems, only a few results have been reported [8, 9] These reported results did not consider the shape of the PSD of all spread signals in the system or the effect of RF input filtering on the receiver In this paper, system capacity supporting multimedia services in MCR-DS/CDMA systems is investigated The number of users per cell is limited by the total interference received at each base station (BS) When a system encounters congestion, admitting a new call can only cause deterioration of the link quality for some active calls and may result in dropping calls Thus, in order to maintain acceptable connections for existing users, a system requires call admission criteria for new call requests Gilhousen et al [0] derived the number of accepted voice calls in order to represent the capacity of CDMA systems Evans and Everitt [] reported results regarding the capacity of multiple service DS-CDMA cellular networks, but they neglected background noise and considered the target signal in the interference Lee et al [2] derived the capacities of single-code and multi-code DS-CDMA systems accommodating multi-class services and also proposed call admission criteria This paper presents capacity estimation for multimedia traffic in MCR-DS/CDMA systems The optimum value of the received power which causes the least interference to other users while maintaining an acceptable QoS requirements is also derived This paper is organized as follows In Section 2, an MCR-DS/CDMA system model is described In Section 3, criteria for capacity estimation in MCR-DS/CDMA systems supporting multimedia services are derived In Section 4, numerical examples are presented and results are discussed Finally, conclusions are given in Section 5 2 System Model 2 MCR-DS/CDMA SYSTEM MODEL In MCR-DS/CDMA systems, as in other cellular systems, a service area is divided into cells, and each cell is served by a BS In each cell, the same RF channels can be reused Therefore, the CDMA system capacity is interference limited [0] A separation of different user signals is achieved by means of signature sequences which are used to spread the spectrum of user information signals A system model is shown in Figure The system consists of several subsystems r chip mj and f mj denote the spreading chip rate and the RF carrier frequency of subsystem {m, j}, m=,,m and j =,, 2 m, respectively Calls are classified into i different classes of bearer services, i =,, I, and the bearer services are arranged in order, according to the required QoS, spreading chip rates, and RF carrier frequencies Table shows an example of relation between three types of calls and class-i bearer service, i =,, 2 The MCR-DS/CDMA system model and the associated assumptions used in this paper are summarized as follow: A service area is divided into cells of equal size

3 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 3 Figure Frequency assignment of an MCR-DS/CDMA system Table Example of relationbetween threetypes of callsand class-i bearer service Type-t Calls Required E b /I o,γ t Class-i Remarks Low γ Subsystem {,}, f resolution 2 Subsystem {2,}, f 2 video 3 Subsystem {2,2}, f 22 2 Facsimile γ 2 4 Subsystem {,}, f 5 Subsystem {2,}, f 2 6 Subsystem {2,2}, f 22 3 Voice γ 3 7 Subsystem {2,}, f 2 8 Subsystem {2,2}, f 22 9 Subsystem {3,}, f 3 0 Subsystem {3,2}, f 32 Subsystem {3,3}, f 33 2 Subsystem {3,4}, f 34 2 Separate frequency bands are used for forward and reverse links Thus, mobile stations experience interference only from BSs and BSs experience interference only from mobile stations 3 Each mobile station is power-controlled by the BS of its home cell 4 A mobile station making a call request to the system chooses its home cell such that the radio propagation attenuation between the mobile station and the BS of its home cell is minimized 5 Only the reverse link is considered because it is more critical to the system capacity than the forward link 6 There are I classes of bearer services with each information bit rate R i and n i bearer services of the class-i (i =,,I) are connected to the BS 7 Given the number of accepted bearer services for each class, the received power at a BS is assumed to be equal for each bearer service in the same class through perfect power control 8 Coherent detection and asynchronous quaternary DS spread-spectrum multiple-access systems are used in additive white Gaussian noise (AWGN) channels

4 32 Young Woo Kim et al 9 Inter-cell interference is assumed to be measured from the received power at the BS 22 QUALITY-OF-SERVICE (QOS) As a QoS measure in an MCR-DS/CDMA system supporting multi-class bearer services, the bit energy-to-interference PSD ratio for class-i bearer service, E b /I o i, is given by: E b /I o i = S i /R i ( I k= λ kin k S k + I i S i ) /( 3 4 Rchip i ) + N o, () where R chip i denotes the chip rate of the spreading sequence of class-i bearer service, S i the received power at the BS, R i the information bit rate, E b the information bit energy, λ ki (0 λ ki ) the interference factor for the class-k bearer service signal to the class-i bearer service signal (refer to subsection 23), n k the number of class-k bearer services transmitting, I i the inter-cell interference received by the BS receiver for the class-i bearer service signals, and N o /2 the two-sided PSD of AWGN Equation () is based on the fact that the bit error rate (BER) is approximately given by BER Q( 2 E b /I o ), whereq(x) = x 2π e y2 2 dy, when coherent detection and asynchronous transmission among multiple user terminals are used in AWGN [3, 4] The coefficient 3 arises in Equation () for the Gaussian approximation because rectangular 4 chip pulses are assumed, and it needs to be changed with the assumption of other chip shapes [5] 23 INTERFERENCE FACTOR, λ ki S k is the power of the class-k bearer service signal (k =,,I) received at a BS The interference factor λ ki (refer to Appendix) is defined as: λ ki S ki S k, (2) where S ki (0 S ki S k ) is the power portion of the class-k bearer service signal received by the BS receiver for the class-i bearer service signal (i =,,I) In the case of using a single RF channel bandwidth, all of the interference factors λ ki are ones ( s) 24 CHARACTERISTICS OF CO-CHANNEL INTERFERENCE IN MCR-DS/CDMA SYSTEMS In order to investigate characteristics of co-channel interference in MCR-DS/CDMA systems, a system model of a two-chip-rate (ie, r chip and r chip 2 ) system shown in Figure 2 [8] is considered The system consists of + 2 m subsystems For convenience, we consider only two types of calls and denote the higher-rate call by type- and the lower-rate call by type-2 In addition, we assume that type- calls are only accommodated in subsystem {,} and type-2 calls in subsystem {m, j} Consider a binary DS-CDMA system with rectangular chip pulses Let n be the number of users in subsystem {, }, n mj be the number of users in subsystem {m, j}; then the n-th transmitted signal of subsystem {, }, s n (t) ( n n ) and the n-th transmitted signal

5 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 33 Figure 2 Frequency assignment of a two-chip-rate system of subsystem {m, j}, s mj n (t) ( n n mj ) are [3] s n (t) = 2P β n (t)α n (t)cos (2πf t + θ n ), (3) s mj n (t) = 2P m β mj n (t)α mj n (t)cos (2πf mj t + θ mj n ) (4) In Equations (3) and (4), the phases introduced by the modulators, θ n and θ mj n, are modeled as iid (independent and identically distributed) random variables uniformly distributed over [0, 2π] The data waveforms β n (t) and β mj n (t) consist of sequences of mutually independent rectangular pulses with duration T = /R and T m = /R m and with equally probable amplitudes +or Since random signature sequences are assumed, the code waveforms α n (t) and α mj n (t) are also sequences of mutually independent rectangular pulses of duration T c = /r chip and T cm = /r chip mj having amplitude + or with the equal probability P and P m are the transmitted powers of type- and type-2 calls, respectively A correlation receiver (or matched filter) is assumed to match the corresponding signal In addition, it is assumed that subsystem {m, j} do not interfere with each other I mj l, m = and l =,,n mj, denotes the interference at the l-th receiver output of subsystem {m, j} [8], then I mj l = n mj n= n =l T m n + Tm 0 T n= m c mj n (t τ mj n )α mj l (t)dt cosφ mj n P Tm c n (t τ n )α mj l (t) cos( 2πF mj t + φ n )dt, (5) P m 0 where c n (t) = β n (t)α n (t); c mj n (t) = β mj n (t)α mj n (t); F mj = f mj f ; φ n = θ n 2πf τ n ;andφ mj n = θ mj n 2πf mj τ mj n τ n and τ mj n are the delays modeled as uniformly distributed random variables in the interval [0,T ] and [0,T m ], respectively It is shown from [6] that φ n and φ mj n are uniformly distributed on [0, 2π] From Equation (5), I mj l is composed of the interference from its own subsystem and that from subsystem {, } Thecos( 2πF mj t + φ n ) term causes different levels of interferences for different values of j Therefore, we know that the farther the carrier frequency f mj is from f, the lower interference the corresponding subsystem can experience

6 34 Young Woo Kim et al 3 Criteria for Capacity Estimation 3 CALL ADMISSION Call admission control is important to prevent the system from becoming overloaded and to maintain an acceptable QoS for existing users BS w is assumed to transmit a pilot signal at a constant power level P (w) on a separate channel at all times When a new user l makes a call attempt, he measures and compares the pilot signal strength of all adjacent BSs User l is assigned to the BS with the strongest pilot signal That is, the new user l is assigned to BS w such that P (w ) h lw = max {P (w) h lw }, (6) w where h lw denotes the gain for user l to BS w After user l is assigned to BS w, a spreading code c is chosen in the set of codes at BS w that are not previously assigned to other users Given the spreading code c, a constraint has to be satisfied: the estimated bit energy-to-interference PSD ratio of the class-i bearer service after admitting the new user cannot be less than γ i, the required bit energy-to-interference PSD ratio for every i (i =,, I) 32 CRITERIA FOR CAPACITY ESTIMATION A new class-i bearer service is accepted at a BS on spreading code c only if S i /R i ( I ) γ i (i =,, I) (7) k= λ kin k S k + I i S i /( 3 4 Rchip i ) + N o Otherwise, the new call is blocked Equation (7) can be rewritten as: I a i S i λ ki n k S k + b i (i =,, I), (8) k= where in general case: a i = + 3G i and b i = 3 4γ i 4 Rchip i N o + I i, in case of using the inter-cell interference factor, f [7]: 3 G i 3 a i = + and b i = 4( + f) γ i 4( + f) Rchip i N o, and G i Rchip i R i denotes the spreading factor The parameter a i is determined according to the spreading bandwidth in a subsystem and QoS requirements of the call Therefore, for the same type of call with different chip rates, the values of a i are different depending on the chip rate In a single RF channel bandwidth system, all of λ ki in Equation (7) are ones ( s)

7 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services CAPACITY ESTIMATION Conditions on the capacity maximization ie, conditions of the minimum transmitted power of the class-i bearer service that still meets the required bit energy-to-interference PSD ratio γ i are achieved when an equality holds in Equation (7) Thus, we have the following constraints on the vectors N =[n,,n I ] and S =[S,,S I ] T that provide the maximum capacity: I a i S i = λ ki n k S k + b i (i =,, I) (9) k= We can rewrite the above constraints as a set of linear equations as follows: (a n λ )S n 2 λ 2 S 2 n I λ I S I = b n λ 2 S + (a 2 n 2 λ 22 )S 2 n I λ I2 S I = b 2 n λ I S n 2 λ 2I S 2 +(a I n I λ II )S I = b I We may write Equation (0) in a matrix form, AS = b, where a n λ n 2 λ 2 n I λ I n λ 2 a 2 n 2 λ 22 n I λ I2 A, n λ I n 2 λ 2I a I n I λ II S b S 2 b 2 S, and b b I S I For a given b, Equation () may be regarded as a system of I linear equations with I unknowns S,, S I and we know from the Fundamental theorem for systems of linear equations that it has a unique solution if and only if an (I I)matrix, A is nonsingular Given the maximum receivable power of the class-i bearer service as S i (i =,, I), the admissible set of network traffic is given by: {(n,n 2,, n I ) S i such that 0 S i S i and S i satisfies Equation ()} (2) Here, the maximum receivable power of the class-i bearer service means the maximum power that can be received by the BS even in the case of the largest propagation loss between the BS and the mobile station In addition, S i implies the optimum received power causing the least interference to other signals while maintaining an acceptable bit energy-to-interference PSD ratio, which can be obtained from Equation (2), given existing calls 4 Numerical Results and Discussion We now show examples of how system capacities can be estimated, given some parameters In addition, characteristics of co-channel interference between subsystems are investigated (0) ()

8 36 Young Woo Kim et al Table 2 Required performance for multi-class services Type-t Calls Information bit rate Required BER Required E b /I o,γ t Low resolution video 28 kb/s (= 96 db) 2 Facsimile 64 kb/s (= 84 db) 3 Voice 32 kb/s (= 68 db) Consider the following three types of calls, as shown in Table 2, where we refer to [8] for the required BERs For simplicity, we consider only a single cell environment We assume N o = 0 4 mw/hz and S i =0 3 mw 4 SYSTEM CAPACITY In order to compare the capacity of an MCR-DS/CDMA system with that of an one-chiprate system, we consider an MCR-DS/CDMA system with two chip rates (ie, r chip =5 Mchips/s and r chip 2 = 25 Mchips/s) and five subsystems (ie, m = 3) in total, as shown in Figure 2 In the MCR-DS/CDMA system, a 5 MHz bandwidth channel can be allocated for RF channels for video, facsimile, and voice calls and 25 MHz bandwidth channels for voice calls Therefore, we assume R chip 2 3 = r chip = r chip = 5 Mchips/s and R chip = r chip 2 = r chip 3j = 25 Mchips/s In addition, we assume R chip 2 3 = r chip = 5 Mchips/s in the one-chip-rate system We can obtain the parameters a i and b i in Equation (8) in Table 3 Next, the interference factors λ ki are considered in Appendix, which are summarized in Table 4 MCR-DS/CDMA System: We may write matrix A in Equation () a n λ n 2 λ 2 n 7 λ 7 n λ 2 a 2 n 2 λ 22 n 7 λ 72 A = n λ 7 n 2 λ 27 a 7 n 7 λ n n 2 n 7 n 9472 n 2 0 = 0076n n 7 One-Chip-Rate System: A = a n n 2 n 3 n a 2 n 2 n 3 n n 2 a 3 n 3 = 422 n n 2 n 3 n 9472 n 2 n 3 n n n 3

9 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 37 Table 3 Parameters Type-t Calls Class-i MCR-DS/CDMA system One-chip-rate system Remarks a i b i a i b i Low resolution video Subsystem {,} 2 Facsimile Subsystem {,} 3 Voice Subsystem {,} Subsystem {3,} Subsystem {3,2} Subsystem {3,3} Subsystem {3,4} Table 4 The interference factors, λ ki k \ i Figure 3 shows the admissible sets (or capacities) for an MCR-DS/CDMA system and an one-chip-rate system N (= n ), N 2 (= n 2 ),andn 3 (= n 3 ) are the admissible numbers for video, facsimile, and voice call, respectively Each admissible point (N,N 2,N 3 ) within the admissible set means the admissible number of each type of calls that the system can support at a specified level of QoS Figure 3 Admissible sets: (a) MCR-CDMA system; (b) One-chip-rate system

10 38 Young Woo Kim et al Table 5 Admissible sets Items MCR-DS/CDMA system One-chip-rate system Number of admissible points Figure 4 MCR-DS/CDMA system model for simulation In Table 5, the admissible points in admissible sets are summarized From the result, it is shown that the MCR-DS/CDMA system supports at least 36% more capacity than the onechip-rate system 42 CHARACTERISTICS OF CO-CHANNEL INTERFERENCE BETWEEN SUBSYSTEMS In order to investigate characteristics of co-channel interference between subsystems, we consider an MCR-DS/CDMA system with three chip rates (ie, r chip, r chip 2,andr chip 3 )andseven subsystems, as shown in Figure 4 The PSDs of DS waveforms in a system configuration are shown in Figure 5 The PSD of each spreading signal follows a curve of sinc 2 {2(f f c )T c }, Figure 5 Psd of DS waveforms in a system configuration

11 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 39 Table 6 Parameters Type-t Calls Class-i a i b i Remarks Low resolution Subsystem {,} video Subsystem {2,} 2 Facsimile Subsystem {2,} Subsystem {3,} Subsystem {3,2} Subsystem {3,3} Subsystem {3,4} 3 Voice Subsystem {2,} Subsystem {3,} Subsystem {3,2} Subsystem {3,3} Subsystem {3,4} (T c : chip duration, f c : carrier frequency) with a rectangular chip pulse Considering both PSD over an RF band and the effect of RF input filtering on the receiver, admissible sets in the following four cases are estimated and the characteristics of co-channel interference between subsystems are investigated: Case-: Using subsystem {,}, subsystems {2,} and {3,}, Case-2: Using subsystem {,}, subsystems {2,} and {3,2}, Case-3: Using subsystem {,}, subsystems {2,} and {3,3}, Case-4: Using subsystem {,}, subsystems {2,} and {3,4} We consider that 5 MHz bandwidth channels can be allocated for RF channels for voice and facsimile calls, a 0 MHz bandwidth channel for voice, facsimile, and video calls, and a 20 MHz bandwidth channel for video calls Therefore, we assume that R chip = r chip = 20 Mchips/s, R chip = r chip 2 = 0 Mchips/s, and R chip = R chip = r chip 3 = 5 Mchips/s The parameters a i and b i are shown in Table 6 and the interference factors λ ki are summarized in Table 7 Finally, we may write matrix A in Equation () Case-: A = = a n λ n 2 λ 2 n 9 λ 9 n λ 2 a 2 n 2 λ 22 n 9 λ 92 n λ 9 n 2 λ 29 a 9 n 9 λ n n 2 n 9 05n 7442 n 2 n n 05n n 9

12 40 Young Woo Kim et al Table 7 Interference factors k \ i Case-2: A = 3884 n n 2 n 0 05n 7442 n 2 n n 05n n 0 Case-3: A = 3884 n n 2 n 05n 7442 n 2 n 04284n n Case-4: A = 3884 n n 2 n 2 05n 7442 n 2 n n n 2 Figure 6 and Table 7 show the admissible sets in case-, case-2, case-3, and case-4 In Figure 6, N (= n +n 2 ), N 2 (= n 3 + +n 7 ),andn 3 (= n 8 + +n 2 ) are the admissible numbers for video, facsimile, and voice call, respectively The admissible set in each case is given by simulations Each admissible point (N,N 2,N 3 ) within the admissible set means the admissible number of each type of calls that the system can support at a specified level of QoS The number of admissible points in case-2 is approximately 55% less than in case-4, and the capacity boundaries in cases -2 and -3 are more similar to that in one-chip-rate system, than the capacity boundaries in other cases This is because mutual-interferences in cases -2 and -3

13 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 4 Table 8 Admissible sets Items Case- Case-2 Case-3 Case-4 Number of admissible points (= N) 3,590 3,379 6,007 7,568 Proportion (= N N in case-4 ) Figure 6 Admissible sets: (a) case-, (b) case-2, (c) case-3, (d) case-4 are larger than in other cases Then, it can be observed that subsystem {3,2} (or {3,3}) suffers more interferences from subsystem {,} than does subsystem {3,} (or {3,4}), as shown in Figure 5 In addition, subsystems {2,j}, (j =, 2) (or {3,j}, (j =,, 4)) interfere with each other by way of subsystem {,}, which yields a change in the number of admitted users in subsystems, 2, and 3 From these observations, it is noted that adjusting the allocation of the number of calls to subsystems can reduce the blocking probability in MCR-DS/CDMA systems 5 Conclusions System capacity and optimum received power in MCR-DS/CDMA systems supporting multimedia services are considered In addition, in order to account for other user interference in the same frequency band, interference factor λ ki in the requirement is introduced Numerical results show that MCR-DS/CDMA systems support more capacity than one-chip-rate

14 42 Young Woo Kim et al Figure 7 PSD and Bandpass filters: (a) PSD of QPSK spreading signal; (b) Transfer function of ideal output filter in a transmitter; (c) PSD of output signal in a transmitter; (d) Transfer function of ideal input filter in a receiver; (e) PSD of input signal in a receiver system and that subsystems {3,j}, (j =,, 4) experience different interferences from subsystem {,} From the results, system performance is strongly affected by a selected channel assignment strategy Therefore, it is important to efficiently assign radio resources in MCR-DS/CDMA systems that support high capacity with a low blocking rate [9] Appendix A Interference Factors In this appendix, we first review the PSD and the autocorrelation function of power signals, and then derive interference factors A POWER SPECTRAL DENSITY AND AUTOCORRELATION FUNCTION The PSD of QPSK spreading signal is expressed in the form of S g (f ) = sinc 2 {2(f f )T c }, (T c : chip duration, f : carrier frequency) with a rectangular chip pulse, as shown in Figure 7 It is often convenient to work with filters having idealized transfer functions with rectangular response functions that are constant within the passband and zero elsewhere Within the passband, a linear phase response characteristic is assumed Thus, /T c and /T c3 = /4T c are the bandwidths of the filters, the transfer functions of these two filters can be written as follows: H o (f ) = [ {(f f )T c }]e jwt o, (3) H i (f ) = [ {4(f f 3 )T c }]e jwt o, (4)

15 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 43 where H o (f ) denotes the transfer function of transmitter output bandpass filter and H i (f ) the transfer function of receiver input bandpass filter Then, the PSD of the output signal in the transmitter, S i (f ) is expressed by: S i (f ) = H o (f ) 2 S g (f ) (5) Finally, the PSD of the input signal in the receiver, S(f) is as follows: S(f) = H i (f ) 2 S i (f ) = H i (f ) 2 H o (f ) 2 S g (f ) = {(f f )T c } 2 {4(f f 3 )T c } 2 sinc 2 {2(f f )T c } (6) By the Wiener Khinchine theorem, which says that the autocorrelation function of a signal and its PSD are Fourier transform pairs, the autocorrelation function R(τ) is obtained by: R(τ) = F [S(f)] = F [ {(f f )T c } 2 {4(f f 3 )T c } 2 sinc 2 {2(f f )T c }] = f 4T c {(f f )T c } 2 {4(f f 3 )T c } 2 sinc 2 {2(f f )T c }e j2πf τ df f 2T c sinc 2 {2(f f )T c }e j2πf τ df (7) The total average power R(0) is given by: R(0) = f 4T c f 2T c sinc 2 {2(f f )T c }df (8) A2 INTERFERENCE FACTORS From the results of the previous subsection A, we can obtain the total power of transmitted signal R(0) t as follows: R(0) t = f + 2T c f 2T c sinc 2 {2(f f )T c }df (9) The power portion of section I, R(0) is given by: R(0) = f 4T c f 2T c sinc 2 {2(f f )T c }df (20) The power portion of section II, R(0) 2 is written as: f R(0) 2 = sinc 2 {2(f f )T c }df (2) f 4T c The power portion of section III, R(0) 3 is given by: R(0) 3 = f + 4T c f sinc 2 {2(f f )T c }df (22)

16 44 Young Woo Kim et al The power portion of section IV, R(0) 4 is written as: R(0) 4 = f + 2T c f + 4T c sinc 2 {2(f f )T c }df (23) From the previous subsection 23, we can determine the interference factors as follows: λ = R(0) t =, R(0) t λ 2 = R(0) t =, R(0) t λ 3 = R(0) t =, R(0) t λ 4 = R(0) R(0) t = 0076, λ 5 = R(0) 2 R(0) t = 04284, λ 6 = R(0) 3 R(0) t = 04284, and λ 7 = R(0) 4 R(0) t = 0076 In a similar way, we can obtain the remaining interference factors The interference factors for each case are shown in Tables 4 and 7 References PG Andermo and LM Ewerbring, A CDMA-Based Radio Access Design for UMTS, IEEE Personal Commun, Vol 2, No, pp 48 53, LB Milstein, DL Schilling, RL Pickholtz, V Erceg, M Kullback, EG Kanterakis, DS Fishman, WH Biederman and DC Salerno, On the Feasibility of a CDMA Overlay for Personal Communications Networks, IEEE J Select Areas Commun, Vol 0, No 4, pp , E Dahlman and K Jamal, Wide-Band Services in a DS-CDMA Based FPLMTS System, in Proc IEEE VTC, April 996, pp C-L I and RD Gitlin, Multi-Code CDMA Wireless Personal Communication Networks, in Proc IEEE ICC, June 995, pp A Baier, UC Fiebig, W Granzow, W Koch, P Teder and J Thielecke, Design Study for a CDMA-Based Third-Generation Mobile Radio System, IEEE J Select Areas Commun, Vol 2, No 4, pp , R E Fisher, A Fukasawa, T Sato, Y Takizawa, T Kato and M Kawabe, Wideband CDMA System for Personal Communications Services, in Proc IEEE VTC, April 996, pp S C Bang, ETRI IMT-2000 Multiband CDMA System for Terrestrial Environments, Mobile Comm Research Div, ETRI, Taejon, Korea, T H Wu, Issues in Multimedia Packet CDMA Personal Communication Networks, PhD Thesis, Dept of Elec Eng, Univ of Maryland, College Park, Aug D Lyu, I Song, Y Han and HM Kim, Analysis of the Performance of an Asynchronous Multiple-Chip- Rate DS/CDMA System, Int J Electron Commun, Vol 5, Issue 4, pp 23 28, KS Gilhousen, IM Jacobs, R Padovani, AJ Viterbi, LA Weaver and CE Wheatley, On the Capacity of a Cellular CDMA System, IEEE Trans Veh Technol, Vol 40, No 2, pp , 99

17 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 45 J Evans and D Everitt, Call Admission Control in Multiple Service DS-CDMA Cellular Networks, in Proc IEEE VTC, April 996, pp SJ Lee, HW Lee and DK Sung, Capacities of Single-Code and Multi-Code DS-CDMA Systems Accommodating Multi-Class Services, IEEE Trans Veh Technol, to be published 3 MB Pursley, Performance Evaluation for Phase-Coded Spread-Spectrum Multiple-Access Communication-Part I: System Analysis, IEEE Trans Commun, Vol 25, No 8, pp , RL Pickholtz, LB Milstein and DL Schilling, Spread Spectrum for Mobile Communications, IEEE Trans Veh Technol, Vol 40, No 2, pp , 99 5 E Geraniotis and B Ghaffari, Performance of Binary and Quaternary Direct-Sequence Spread-Spectrum Multiple-Access Systems with Random Signature Sequences, IEEE Trans Commun, Vol 39, No 5, pp , 99 6 MB Pursley, Spread-Spectrum Multiple-Access Communications, in G Longer (ed), Multi-User Communication Systems, Springer-Verlag: New York, NY, pp 39 99, 98 7 AM Viterbi and AJ Viterbi, Erlang Capacity of a Power Controlled CDMA System, IEEE J Select Areas Commun, Vol, No 6, pp , P Mermelstein, A Jalali and H Leib, Integrated Services on Wireless Multiple Access Networks, in Proc IEEE ICC, Oct 993, pp Young W Kim, Seung J Lee, Min Y Chung, Jeong H Kim and Dan K Sung, Radio Resource Assignment in Multiple-Chip-Rate DS/CDMA Systems Supporting Multimedia Services, IEICE Trans Commun, Vol E82-B, No, pp 45 55, 999 Young Woo Kim received the BS degree in electronic engineering from Korea Aviation College in 977 and the MS degree in electronic engineering from Seoul National University in 983 He is working towards the PhD degree in electrical engineering at Korea Advanced Institute of Science and Technology (KAIST) since 994 From Dec 978 to Feb 985, he was a development engineer with Oriental Precision Company, Korea, where he had been engaged in research and development of military communication systems Since March 985, he has been with Hyundai Electronics Industries Company, Korea His research interests include radio resource management and call admission control in IMT-2000 He is a member of KICS

18 46 Young Woo Kim et al Seung Joon Lee received the BS, MS, and PhD degrees in electrical engineering from KAIST, in 99, 993, and 998, respectively He has been with Hyundai Electronics Industries Company, Korea since Nov 994 His research interests include handoff schemes in wireless ATM and support of multimedia in CDMA systems He is a member of IEEE and KICS Jeong Ho Kim received the BS and MS degrees in electrical engineering from KAIST, in 99 and 993, respectively Currently he is working towards the PhD degree in electrical engineering at KAIST He has been with LG Electronics Inc, Korea since Feb 993 His research interests include system analysis, power control, and multimedia multiple access protocol in CDMA systems He is a student member of IEEE and a member of KICS

19 Capacity Estimation in MCR-DS/CDMA Systems Supporting Multimedia Services 47 Young Hoon Kwon received the BS degree in electronics from Kyungpook National University in 994 and the MS degree in electrical engineering from KAIST in 996 He is working towards the PhD degree in electrical engineering at KAIST since 996 His research interests include IMT-2000 network and satellite communications He is a student member of IEEE Dan Keun Sung received the BS degree in electronic engineering from Seoul National University in 975, the MS and PhD degrees in electrical and computer engineering from University of Texas at Austin, in 982 and 986, respectively From May 977 to July 980, he was a research engineer with the Electronics and Telecommunications Research Institute, where he had been engaged in research on the development of electronic switching systems In 986, he joined the faculty of the Korea Institute of Technology and is currently a Professor of Dept of Electrical Engineering at KAIST His research interests include ISDN switching systems, ATM switching systems, wireless networks, and performance and reliability of systems He is a member of IEEE, IEICE, KITE, KICS and KISS