The Interference on Wcdma System in 3g Coexistence Network

The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’06)

1-4244-0330-8/06/$20.00 c ∨2006 IEEE

THE INTERFERENCE ON WCDMA SYSTEM IN 3G COEXISTENCE NETWORK

Muhammad Suryanegara Edwardo Rizky Hutabarat Dadang Gunawan

Dept. of Electrical Engineering Dept. of Electrical Engineering Dept. of Electrical Engineering University of Indonesia University of Indonesia University of Indonesia

Jakarta, Indonesia Jakarta, Indonesia Jakarta, Indonesia

ABSTRACT

The coexistence network of different 3G technologies (WCDMA and CDMA2000) requires analysis of its adjacent channel interference. In this paper, we investigated the interference on WCDMA system that caused by CDMA2000 network. Several scenarios and calculation models were applied to measure impacts on uplink and downlink scheme. The results showed that interference from CDMA2000 influence WCDMA performance significantly. Distance between coexistence terminals (MS and BS), their number, and guard band frequency determined minimum allowed received power at WCDMA BS and SIR in WCDMA MS, which lead to capacity degradation.

I. INTRODUCTION

The 3G WCDMA and CDMA2000 systems come with higher bandwidth and bitrate, providing multimedia services such as audio/video streaming, teleconferencing, etc [1]. Both use CDMA as the multiple access technique, which is typically interference limited. The Interference might disturb transmission and receiving process of cellular signals at its terminals : Node B / Base Station (BS) and Mobile Station (MS).

In the development of 3G mobile network, WCDMA and CDMA2000 as two different type of systems might be deployed in adjacent frequency bands in the same area. This phenomenon is called coexistence network, leading to an interference problem. Inter-interference can occurs because of lack of RF isolation, which results in the capacity degradation of both systems [2].

One of the problems in the deployment of 3G systems happened in developing countries is the coexistence network of different 3G technologies. In this paper, we investigated the coexistence of WCDMA and CDMA2000 systems that was practically happened in Indonesia. Since the regulator has decided to implement single 3G technology, namely WCDMA, our work only focused to the effect of interference on WCDMA system that caused by CDMA2000 network. The calculation and simulation were evaluated in the uplink and downlink schemes.

II. COEXISTENCE OF WCDMA AND CDMA2000

A. Interference Source

The sources of interference can be classified as in-band and out-band interference [3]. Main in-band interference sources are the intra-cell interference due to multiple access or users

operating in the same cell, and the inter-cell interference due to users or base station operating in the same band but placed in the different cell.

The out-band interference source is the adjacent channel interference (ACI) generated by other cellular signals in the adjacent frequency bands. The existence of ACI is mainly because of non-linearity of power amplifier or non-ideal filtering in receiver [3]. Hence, it can lead to significant reduction in its neighbour system capacity.

Our work calculated and simulated phenomena in one cell scenario, where 1 (one) WCDMA Base Station (BS) – refer to 3G Node B - serving numbers of WCDMA Mobile Station (MS). This cell was affected by CDMA2000 BS and number of CDMA2000 MS as adjacent channel interferer. The work was using parameters summarized in Table 1.

Table 1: Parameters of Calculations

Parameter Value Chip Rate (W )

38.4 Megachips/sec

Thermal Noise (N) -103 dBm, -99dBm User bit-rate (R) 12.2 kbps (speech) Voice activity factor ( v ) 0.5 Eb/No target (ρ ) 4.9 dB Other-to-own-cell interference ratio ( fUL )

0.55

Guard Band 5 MHz , 10 MHz Transmissión Power of CDMA2000 MS (P TxI )

21 dBm

Other-to-own-cell interference ratio (f UL) 0.6

The distance between CDMA2000 MS and WCDMA BS 50 m – 500 m

Orthogonality factor (α) 0.4 Transmission Power of CDMA2000 BS (PTx BS) 40 dBm

B. Uplink Calculations There are two calculations in uplink scheme, measured by varying distance, guarband frequency, and number of CDMA2000 MS. It was designed by setting CDMA2000 MS as source of interferer. The first calculation aimed to get minimum allowed received power at WCDMA BS, while the second one provide its capacity degradation.

1) Calculation of the minimum allowed received

power at WCDMA BS

The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’06

Following are algorithm to calculate minimum allowed received power at WCDMA BS.

1. Calculating the maximum capacity or pole capacity that can be served by WCDMA system by using (1) [5].

(1)

2. Calculating the minimum allowed received power at WCDMA BS before the presence of interference from CDMA2000 MS, by substituting parameters into (2).

(2)

3. Calculating the interference power from 1 (one) CDMA2000 MS by using (3). The ACIR value is appropriate to the guard band used in calculation. ACIR value for 5 MHz guard band is 32.7 dB and for 10 MHz guard band is 42.2 dB.

PRxI = PTxI – ACIR – PathLoss (dBm) (3)

The propagation model used in calculation was Free Space Loss with 3G frequency carrier ( fc ) 1950 MHz. The pathloss was measured by using (4). We set distance between WCDMA BS and CDMA2000 MS to be 500 m and 1000 m.

PathLoss = 38,25+ 20.log10[distance(m)] (4)

4. Calculating the total interference power from CDMA2000 MS. The interference power from every CDMA2000 MS was assumed to be equal so the total interference power can be derived from (5).

ICDMA2000 (Watt) = Number of CDMA2000 MS x PRxI (5)

We set number of CDMA2000 MS to be 1, 5, 10 and 100 . 5. Calculating the minimum allowed received power at

WCDMA BS after the presence of the CDMA2000 MS by judging ICDMA2000 , as shown in (6).

(6)

Afterward, we plot the minimum allowed received power at the WCDMA BS with and without interference, by varying number of WCDMA MS.

2) Calculation of the Capacity Loss.

The steps to measure capacity loss are on the following.

1. Calculating WCDMA capacity (kint) when WCDMA BS has been interfered by CDMA2000 MS. In order to attain specific trend, we only varied distance factor from 50 to 500 m and number of CDMA2000 to be 10 and 100 MS. The results were obtained by using (7)

(7)

2. Calculating the percentage of capacity loss by using (8).

(8)

C. Downlink Calculations

The simulation of downlink calculation was to measure capacity degradation of WCDMA MS because of the presence of CDMA2000 BS. It is reflected from SIR (Signal-to-Interference Ratio) of WCDMA MS, where satisfied criteria is 5 % from the SIR target [6]. Simulation was designed in one cell scenario, that 1 (one) WCDMA BS served numbers of its users (WCDMA MS). The work set CDMA2000 BS as source of interferer.

The WCDMA downlink simulation are as follow : 1. Distributing number of WCDMA MS (users) randomly in

one cell. 2. Defining the position of one CDMA2000 BS and its

distance to the WCDMA BS. 3. Calculating pathloss value for each WCDMA MS

towards WCDMA BS and CDMA2000 BS. 4. Calculating total transmission power (PTot) of WCDMA

BS by using (9).

(9)

5. Calculating the allocated transmission power for every WCDMA MS before the presence of the CDMA2000 BS by using (10).

(10)

6. Calculating the interference power generated by CDMA2000 BS for each pathloss value from step 3.

7. Calculating the SIR value for every WCDMA MS after the presence of CDMA2000 BS by using (11).

( ) ( )ULfkRW

NbeforeP+−−

=1*1**

*minρν

ρ

( ) 11**

++

=ULf

RW

kρν

( )( ) ( )UL

CDMA

fkR

WIN

afterP+−−

+=

1*1**

*min 2000

ρν

ρ

( )

( )

+∗∗

∗+−

+=UL

CDMA

fpIN

RW

k1

1 beforemin

2000

int ρν

ρ

% 1001losscapacity % int ∗

−=

kk

( )∑

∑

=

=

−∗∗−

∗∗∗

= k

i

k

i

i

Tot

WRW

RNL

P

1

1

11 αρ

ρ

( )( )iToti LNPW

Rp ∗+∗−∗= αρ 1


(11)

8. Evaluating the SIR value for every WCDMA MS. If the SIRnew lower than 5 % of the SIR target value, MS can’t be served by WCDMA BS. The SIR target value is obtained from the multiplication of the Eb/No target with the Processing Gain (W /R).

III. RESULTS AND DISCUSSIONS

A. Uplink Calculations

The calculations generated graphs showing the minimum allowed received power at WCDMA BS for different number of user. The value before and after the presence of interference from CDMA2000 MS, could be compared by observing the graphs.

Figure 1: Minimum allowed received power at WCDMA BS for

certain number of WCDMA users ( using 5 MHz guard band and the average distance between WCDMA BS and CDMA2000 MS is about 1000 m )

Fig. 1 and Fig. 2 show calculation results when distance

between WCDMA BS and CDMA2000 MS was 1000 m by using guardband 5 MHz and 10 MHz consecutively. Both lines figure minimum allowed received power when there were 1, 5, 10 and 100 CDMA2000 MS.

The minimum allowed received power at WCDMA BS can be referred as the coverage threshold [5]. It reflects number of users which can be served in uplink scheme. Results imply interference from CDMA2000 MS increase minimum allowed received power at WCDMA BS, then decrease number of served user. We may also see that quantity of CDMA2000 MS plays significant role. The more number of CDMA2000 MS, cause the addition of minimum allowed received power at WCDMA BS.

0 20 40 60 80 100 120 140

-125

-120

-115

-110

-105

-100

-97

-95

Jumlah User WCDMA

Day

a m

inim

um

di B

TS

(dB

m)

Sebelum interferensi1 MS CDMA20005 MS CDMA200010 MS CDMA2000100 MS CDMA2000

v = 0.5; fUL = 0.55; R = 12.2 kbps Eb/No = 4.9 dB Guard Band 10 MHz


certain number of WCDMA users ( using 10 MHz guard band and the average distance between WCDMA BS and CDMA2000 MS is 1000 m )

0 20 40 60 80 100 120 140-125

-120

-115

-110

-105

-100

-95

-90

-85

-80

Jumlah User WCDMA

Day

a m

inim

um d

i BT

S (d

Bm

)

Sebelum interferensi1 MS CDMA2000 5 MS CDMA2000 10 MS CDMA2000 100 MS CDMA2000


Figure 3: Minimum allowed received power in WCDMA BS for


0 20 40 60 80 100 120 140

-125

-120

-115

-110

-105

-100

-95

-90

Jumlah User WCDMA

Day

a m

inim

um d

i BT

S (d

Bm

)

Sebelum interferensi1 MS CDMA2000 5 MS CDMA2000 10 MS CDMA2000 100 MS CDMA2000




( )

++∗−

=

20001 CDMAi

Tot

i

i

new

INL

PL

p

SIRα

0 20 40 60 80 100 120 140-125

-120

-115

-110

-105

-100

-95

-90

-85

Jumlah User WCDMA

Day

a m

inim

um d

i BT

S (d

Bm

)

Sebelum interferensi1 MS CDMA20005 MS CDMA200010 MS CDMA2000100 MS CDMA2000


Number of WCDMA MS (users)


Without Interference

With Interference

Minim

um allow

ed power at

WC

DM

A B

S (dBm)

Minim

um allow

ed power at

WC

DM

A B

S (dBm)

without interference




Minim

um allow

ed power at

WC

DM

A B

S (dBm)


Minim

um allow

ed power at

WC

DM

A B

S (dBm)



On the other hand, Fig. 2 shows positive impact of additional guardband. By using 10 MHz, there was almost no significant differents for the impact of up to 10 (ten) CDMA 2000 MS, instead of 100 ones.

Fig. 3 and Fig. 4 shows calculation results when distance between WCDMA BS and CDMA2000 MS was made to be 500 m. Results showed that minimum allowed received power at WCDMA BS was bigger compare to 1000 m distance. It implies that distance factor between CDMA2000 MS and WCDMA BS is significant. For any small distance, the interference power would be larger and the number of user served by WCDMA BS become smaller. At 1000m distance and 10 MHz guardband, interference from 100 CDMA2000 MS made -110 dBm WCDMA BS might serve 110 users. Within 500 m distance, it only can serve 65 users, which is a significant reduction.

Results of Capacity Loss calculation are showed in Fig. 5 and Fig. 6.

50 100 150 200 250 300 350 400 450 500

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

Jarak BS WCDMA ke MS CDMA2000 (m)

Cap

acity

Los

s (%

)

R = 12.2 kbps; Eb/No = 4.9 dB Guard Band 5 MHz

Jumlah MS CDMA2000 = 10

Figure 5: Uplink Capacity Loss ( using 5 MHz guard band and the

number of the CDMA2000 MS is 10 users )

50 100 150 200 250 300 350 400 450 5000

2

4

6

8

10

12

14

16

18

20

Jarak BS WCDMA ke MS CDMA2000 (m)

Cap

acity

Los

s (%

)

R = 12.2 kbps; Eb/No = 4.9 dB Guard Band 5 MHz

Jumlah MS CDMA2000 = 100

Fig 6. Uplink Capacity Loss (using 5 MHz guard band and the

number of the CDMA2000 MS is 100 users )

Fig. 5 and Fig. 6 shows capacity loss of WCDMA system when using 5 MHz guard band and number of CDMA2000

MS were 10 and 100 consecutively. The distance reduction between WCDMA BS and CDMA2000 MS may cause larger capacity loss. For only 10 users of CDMA2000 MS, the 50 m distance made WCDMA capacity loss to be 2.1 %. When number of CDMA2000 MS was increased to be 100 users, capacity loss of WCDMA system also increased to be 20 %. The excalation of CDMA2000 MS (users), would cause bigger loss on WCDMA capacity.

B. Downlink Calculations

Simulation results of downlink scheme showed effect of interference generating by CDMA2000 BS, to the distribution of WCDMA MS. Fig. 7 reflects initial condition before interference occurs. WCDMA BS was placed in the center of cell, and 100 users WCDMA MS were distributed randomly. Fig. 8 shows distribution of WCDMA MS when CDMA2000 BS was located outside and near WCDMA cell. Fig. 9 shows the presence of CDMA2000 BS influencing distribution of WCDMA MS. From the figures, we can observe the WCDMA MS which near to the position of CDMA2000 BS are blocked. This cause the degradation in WCDMA performance.

Fig. 9 and Fig. 10 show the distribution of WCDMA MS when position of CDMA2000 BS is inside the cell and near WCDMA BS. Fig 9 is evaluated when using 5 MHz guard band and Fig 10 using 10 MHz. The blocking area of WCDMA MS is proportionate to the addition of guardband frequency.

Figure 7: Distribution of 100 WCDMA MS without the interference

Figure 8: Distribution of 100 WCDMA MS after presence of

interference when the CDMA2000 BS is placed outside the cell

-600 -400 -200 0 200 400 600-600

-400

-200

0

200

400

600

O BS WCDMA

Distribusi MS WCDMA dalam satu sel

MS WCDMA O

-600 -400 -200 0 200 400 600-600

-400

-200

0

200

400

600

O BS WCDMA

MS WCDMA O

Distribusi MS yang masih dijangkau oleh BS WCDMA

BS CDMA2000

O

O

Distance (m) between WCDMA BS and CDMA2000 MS

Distance (m) between WCDMA BS and CDMA2000 MS

WCDMA BS in the center of cell

CDMA 2000 BS

Capacity Loss (percent)

Capacity Loss (percent)



interference when the CDMA2000 BS is placed inside the cell and using 5 MHz guard band


interference when the CDMA2000 BS is placed inside the cell and using 10 MHz guard band

The simulation of downlink produced SIR value representing WCDMA system performance. The SIR value was evaluated on the variation of distance between WCDMA MS and CDMA2000 BS. Fig. 11 shows the SIR value obtained from downlink calculations. When WCDMA MS are closer to the CDMA2000 BS, the SIR value become smaller, which mean interference power of the CDMA2000 BS become larger.

50 100 150 200 250 300 350 400 450 500-20

-15

-10

-5

0

5

10

15

Jarak MS ke BS CDMA2000 (m)

SIR

(dB)

Figure 11 : SIR vs Distance

IV. CONCLUSIONS

We investigated the effect of adjacent channel interference, generated by CDMA2000, on the WCDMA system uplink and downlink scheme. In 3G coexistence network, the presence of CDMA2000 system influenced WCDMA performance. Interference generated by CDMA2000 MS increased the minimum allowed received power at WCDMA BS, then lead to reduction of WCDMA coverage and cause a significant capacity loss. In downlink scheme, interference due to CDMA2000 BS influenced the performance of WCDMA communication system which can be seen from significant reduction of SIR value. The effect of interference depends on several factors including distance between WCDMA and CDMA2000 terminals (BS and MS), number of CDMA2000 MS, interference power, and guard band frequency. The using of guard band should reduce the effect of interference.

ACKNOWLEDGMENT This research was run on the basis of Indonesia 3G

implementation test, in collaboration between Dept. of Electrical Engineering University of Indoneisa and PT TELKOMSEL. Authors thank Program Hibah Kompetisi B (PHK-B) Departemen Teknik Elektro Universitas Indonesia for the financial support.

REFERENCES

[1] Smith, C., Collins, D., 3G Wireless Nertwork, The McGraw-Hill Companies Inc., USA 2002.

[2] Wu Jiang, Liang S., Niu Kai, and Wu Weiling, “Capacity Loss Due to Coexistence of WCDMA and CDMA2000 systems”, Journal, School of Information Engineering Beijing University of Posts and Telecommunications, 2003.

[3] Durantini A., Mazzenga, F., Santella G., “A Semi-Analytic Approach for CDMA Systems Performance Evaluation with Adjacent Channel Interference”, Journal, IEEE, Italy, 2004.

[4] Sigit A., “Interference WCDMA – CDMA2000”, Report, TELKOMSEL Report, September 2005,

[5] Heiska, K., “On The Modelling of WCDMA System Performance with Propagation Data”, Dissertation for the degree of Doctor of Science in Technology, Department of Electrical and Communications Engineering, Helsinki University of Technology, Espoo, Finland, 23 April 2004

[6] 3GPP TR 25.942 V5.1.0, “RF System Scenarios (Release 5)”, Technical Specification Group Radio Access Networks, June 2002

-600 -400 -200 0 200 400 600-600

-400

-200

0

200

400

600

O BS WCDMA

MS WCDMA O


BS CDMA2000

O

O

-600 -400 -200 0 200 400 600-600

-400

-200

0

200

400

600

O BS WCDMA

MS WCDMA O


BS CDMA2000

O

O

Distance (m) between WCDMA MS and CDMA2000 BS

CDMA 2000 BS

CDMA 2000 BS

The Interference on Wcdma System in 3g Coexistence Network

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