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1、3GPP TSG RAN WG1 Meeting #41R1-050507Athens, Greece, 9 13 May, 2005Agenda Item:13.2Source:HuaweiTitle:Soft Frequency Reuse Scheme for UTRAN LTEDocument for:Discussion 1 IntroductionThe objective of UTRA evolution study item is to develop a framework for the evolution of the 3GPP radio-access technol
2、ogy towards a high-data-rate, low-latency and packet-optimized radio-access technology 1. The new requirements on higher spectrum efficiency and increased data rate at the cell edge, along with consideration of alternative transmission technologies such as OFDM, open the question of the frequency re
3、use factor in EUTRA.In this contribution we show some benefits of the so-called soft reuse scheme for the application in the EUTRA along with multi-carrier based transmission technologies, such as OFDM for example. The optimum reuse factor at the cell edge is analysed in Section 2. The soft frequenc
4、y reuse scheme, which is characterised by frequency reuse factor 1 in the central region of a cell, and by frequency reuse factor greater than 1 at the outward cell region close to the cell edge, is defined in details in the Section 3. The benefits of soft reuse scheme are pointed out in section 4.
5、Finally, some conclusions are given in Section 5.2 Frequency Reuse Factor Analysis In a multi-carrier telecommunication system, the frequency reuse can be achieved in 2 ways:1. Carrier method: different carriers in different cell, same to traditional frequency reuse method.2. Sub-carrier method: sam
6、e carrier and different sub-carriers in different cell which illustrated in Fig. 1.In a wireless cellular communication system, the signal to interference ratio (SIR) can be generally described as: (1): the received power of the expected user signal: inner cell interference power : other cell interf
7、erence power: white noise powerWe assume that advanced MA scheme or receiver is used, the intra-cell interference is eliminated, and the SIR representation can be simplified as: . (2)In case of flat fading channel, according to the Shannons theorem, the channel capacity is given as: (3)Fig.1 Sub-car
8、rier frequency reuse schemeTab 1 RF Parameters Used in ComputationParameters ValueComputation Equation Carrier Bandwidth W (MHz)20AWhite noise power density(dBm/Hz)-174BReceiver Noise Figure (dB)5CWhite noise power (dBm)-96D=10*log(A)+B+CTx power (dBm)45ECell Radius (km)1.0FPath loss Model (dB)137.3
9、G137.3 + 35.2*log(F)According the above equations and RF parameters, we calculate the SIR and channel capacity at the cell edge. A 27 cell network is used for computations, as shown in Fig. 2. Mobile stations are located at the intersection of 3 adjacent cells which are represented by the red dot. I
10、n the network, the transmitting power of the serving and interfering cell is 45dBm. Fig.2 Network deployment used in the computationThe SIR and cell edge channel capacity variation with the reuse factor are depicted in the following Fig. 3 and Fig.4 respectively.Fig.3 SIR at the cell edge Fig.4 Chan
11、nel Capacity at the cell edgeFrom the above two Figures, some arguments are listed below:1. Smaller the reuse factor corresponds to larger available bandwidth for each cell, and lower signal to interference (SIR) due to co-channel interference. On the contrary, larger reuse factor corresponds to sma
12、ller available bandwidth and higher SIR.2. In the case of reuse factor is 1 or 2, due to the co-channel interference from the adjacent cell, the SIR at cell edge are -4.4dB and -1.1dB respectively, which are very low. This is the reason for a low channel capacity at the cell edge, which are 89Mbps.3
13、. In the case of reuse factor is 3, due to the elimination of co-channel interference from the adjacent cell, there is an obvious improvement in the SIR at the cell edge. The SIR value reaches 5.89dB in the computation example. Although the available bandwidth is 1/3 of the total bandwidth, the gain
14、 in SIR can counteract the loss in the bandwidth; the channel capacity reaches 15Mbps, which is near double of the capacity at the case of reuse factor 1.4. With the increase of reuse factor, the co-channel interference continues to decrease, and so the SIR continues to improve. However, the increme
15、nts of SIR can not counteract the loss in bandwidth, so the channel capacity decreases. 5. In the computation example, the intra-cell interference is not considered. Here, the assumption is that the intra-cell interference can be eliminated by advanced multiple access scheme such as OFDM, MC-CDMA and advanced receiver algorithm such as frequency domain equalizer, etc. The main noise comes mainly from co-channel interference from other cell and white
