Wcdma for umts radio access for third genergation mobile communacations phần 10 ppsx

The 3GPP standard and implementation costs of the receiver set basic requirements for a PIC receiver. The strong channel coding specified in the standard and usually short spreading factor mean that SINR can be quite low at a receiver, resulting in unreliable tentative decisions and high BER before decoding, up to 15 %. This means that the hard decision- based PIC cannot work very well, since for every wrong decision, the corresponding interference is doubled. SQ-PIC tries to overcome this by using a reliability measure to weight the tentative decisions as mentioned. In order to minimise costs, only one PIC stage is suggested as the performance improvement from the second or third stage is not that large. 12.6.2.3 PIC Efficiency and Derivation of Network Level Gains We define PIC efficiency  as the amount of own-cell interference it can remove. (It is assumed that PIC cannot remove other inter-cell interference.) We can write I total for Rake and PIC as I total;rake ¼ I own þ iI own þ N 0 ¼ð1 þ iÞK rake P j þ P N ð12:26aÞ I total;PIC ¼ð1 À ÞI own þ iI own þ N 0 ¼ð1 þ i À ÞK pic P j þ P N ð12:26bÞ where i is the ratio of other-cell interference to own-cell interference, P N is the thermal noise power and we have assumed that users are homogenous, each having the same received power P j . K rake and K pic are the number of users for Rake and PIC, respectively. K pic is selected so that I total,rake and I total,pic are equal i.e. noise rises of Rake and PIC are the same. We can solve capacity gain G cap ¼ K pic /K rake from the equations above: G cap ¼ K pic K rake ¼ 1 þ i 1 þ i À  ð12:27Þ Coverage gain is defined as the ratio of required E b =N 0 s for Rake and PIC when the number of users, K, is kept constant: G cov ¼ E b =N 0 fg rake E b =N 0 fg pic ð12:28Þ Using the definition of E b =N 0 and using Equations (12.26) we get: E b =N 0 fg K ¼ W R P j P N ¼ W R 1 1 L j À 1 þ i À ðÞK ð12:29Þ Note that  is zero for a Rake receiver. From Equations (12.28) and (12.29) we obtain: G cov ¼ E b =N 0 fg rake E b =N 0 fg pic ¼ W R 1 1 L j À 1 þ iðÞK W R 1 1 L j À 1 þ i À ðÞK ¼ 1 L j Àð1 þ i À ÞK 1 L j Àð1 þ iÞK ð12:30Þ We can solve K from the noise rise equation, Equation (8.9): K ¼ 1 L j À 1 L j ÁI rake 1 þ i ð12:31Þ Physical Layer Performance 403 where Á I rake is the noise rise with a Rake receiver. We can now solve G cov as a function of i,  and ÁI rake : G cov ¼ 1 þ  Á ÁI rake À 1ðÞ 1 þ i ð12:32Þ Examples of the capacity gain in Equation (12.27) and the coverage gain in Equation (12.28) as functions of i are depicted in Figure 12.56 and Figure 12.57. In coverage gain examples, the noise rise of rake ÁI rake is also a parameter. The gains increase as i decreases, which is 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 20 40 60 80 100 120 i G cap (%) β = 0.5 β = 0.4 β = 0.3 Figure 12.56. Capacity gain of PIC as a function of i with PIC efficiency  as a parameter 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 1 2 3 4 I rake = 3 dB G cov i (dB) 6 dB I rake = β ∆ ∆ = 0.5 = 0.4 β = 0.3 β Figure 12.57. Coverage gain of PIC as a function of inter-cell interference i, multiuser efficiency  and noise rise ÁI Rake 404 WCDMA for UMTS expected since PIC cannot cancel other-cell interference. The gains naturally also depend on . The dependence is particularly strong in single cell without any other-cell interference, i ¼ 0. Coverage gain also depends on the target noise rise with a Rake receiver: the higher the interference level without PIC, the higher the gain from PIC. 12.6.2.4 Performance of SQ-PIC The performance of SQ-PIC was evaluated by Monte Carlo simulations in the link level without inter-cell interference [74]. Two propagation channels were considered, namely a pedestrian type of environment (Case 1 in 3GPP TS 25.141) and a vehicular type of environment (Case 3 in 3GPP TS 25.141). In the pedestrian channel, the UE velocity was 3 km/h, and in the vehicular channel, 120 km/h. The 12.2 kbps speech and 384 kbps data services were studied. We estimate the PIC efficiency  from the simulation results by finding the value of  that gives the best fit to the simulation results. The results are shown in Table 12.23. The PIC efficiency is between 24 % and 41 %. The highest efficiency is obtained at high mobile speed with high data rate 384 kbps. The fast power control cannot keep the received power level exactly constant at high speed and there are larger power differences that can be cancelled by PIC. A high data rate provides better efficiency, since the number of simultaneous users is lower and the number of estimated parameters by PIC is lower, resulting in more accurate estimates. With a data service, the small spreading factor results also in high cross correlation between users, making the performance of Rake poor and hence allowing higher potential gain for SQ-PIC. The lowest gain is obtained at low mobile speed with voice users. Table 12.24 shows capacity and coverage gains with the estimated efficiencies. The capacity gains are 26–35 % in a typical macro cell with i ¼ 0.55. The coverage gain is 1.6–2.5 dB. This coverage gain assumes an initial noise rise of 6 dB. If the initial noise rise was 3 dB, the corresponding coverage gain would be 0.6–1.0 dB. Numerical results for a data service are depicted in Figure 12.58 for channel case 3. The number of diversity antennas was one, two or four for both Rake and SQ-PIC. Rake with diversity antennas can be seen as an alternative to PIC, since increasing the order of diversity also provides substantial gains. The reason for this is Rake’s ability to average MAI over diversity antennas, as the interference components from different diversity channels are independent. The results show that increasing the number of antennas with a Rake receiver Table 12.23. PIC efficiency PIC efficiency  Number of diversity ————————————————— Propagation channel antennas (M) 384 kbps data 12.2 kbps speech Case 1 v ¼ 3 km/h 1 32 % 24 % 2 36 % 26 % 4 37 % 33 % Case 3 v ¼ 120 km/h 1 40 % 35 % 2 41 % 32 % 4 36 % 28 % Physical Layer Performance 405 provides higher capacity and better coverage than introducing PIC. In the case of a low number of users, the gain from any interference cancellation is low, while more antennas provide clear coverage benefits. On the other hand, adding more antennas and antenna cables may not be possible from the site solution point of view, while the introdu ction of interference cancellation as the baseband processing enhancement is easier. Interference cancellation, namely SQ-PIC, is the most promising method for improving base station receiver performance, as well as system capacity and coverage. Uplink interference cancellation may provide further gains in end user throughput when the uplink Table 12.24. Capacity and coverage gains with simulated PIC efficiencies (with outer-to-own cell interference ratio i ¼ 0.55) Coverage gain (dB) with Capacity gain ( %) 6 dB noise rise ——————————— —————————— 384 kbps 12.2 kbps 384 kbps 12.2 kbps Propagation channel M data speech data speech Case 1 v ¼ 3 km/h 1 26 % 26 % 2.1 dB 1.6 dB 2 30 % 30 % 2.3 dB 1.8 dB 4 31 % 31 % 2.3 dB 2.1 dB Case 3 v ¼ 120 km/h 1 35 % 35 % 2.5 dB 2.2 dB 2 36 % 36 % 2.5 dB 2.1 dB 4 30 % 30 % 2.3 dB 1.9 dB 0 5 10 15 20 25 30 35 −5 0 5 10 15 20 1 ant 2 ant 4 ant Required E b / N 0 (dB) K Rake, sim. SQ-PIC, sim Rake, theory PIC,theory β =0.4 β =0.41 β =0.36 Figure 12.58. Required E b =N 0 vs. number of users for a 384 kbps data service and BLER target 10 % in case 3 channel (120 km/h), the number of diversity antennas 1, 2 and 4 406 WCDMA for UMTS peak data rates exceed 1 Mbps in High-Speed Uplink Packet Access, HSUPA, which is a 3GPP study item in Release 6. For more details see Chapter 11. 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[74] Vihria ¨ la ¨ , J. and Horneman, K., ‘Impacts of SQ-PIC to Capacity and Coverage in WCDMA Uplink’, to appear in ISSSTA’04, September 2004. 410 WCDMA for UMTS 13 UTRA TDD Modes Antti Toskala, Harri Holma, Otto Lehtinen and Heli Va ¨ a ¨ ta ¨ ja ¨ 13.1 Introduction The UTRA TDD modes are intended to operate in the unpaired spectrum, as shown in Figure 1.2 in Chapter 1, illustrating the spectrum allocations in various regions. As can be seen from Figure 1.2, there is no TDD spectrum available in all regions. The background of UTRA TDD was described in Chapter 4. During the standardisation process in ETSI and 3GPP, the major parameters were harmonised between UTRA FDD and TDD modes, including chip rate of 3.84 Mcps and modulation, for the Release ’99 specifications. During the Release 4 work, the low chip rate TDD with 1.28 Mcps (TD-SCDMA) was introduced, following the same principles as the 3.84 Mcps TDD but with a few additional features, such as uplink synchronisation, as well as the mandatory differences arising from the different chip rate. Both TDD modes are covered in the physical layer specifications for the 3rd Generation Partnership Project (3GPP), the documents TS 25.221–TS 25.224 and TS 25.102 [1–5] are especially valuable references for obtaining information on the exact details. For Release 5, the High-Speed Downlink Packet Access (HSDPA) presented for FDD in Chapter 11 has been included for TDD as well. The TDD operation of HSDPA includes similar ARQ operation, use of 16 QAM modulation and fast Node B based scheduling, as described in Chapter 11. This chapter first introduces TDD as a duplex method on a general level. The physical layer and related procedures of the UTRA TDD modes are introduced in Section 13.2. UTRA TDD interference issues are evaluated in Section 13.3. The HSDPA operation principles with TDD modes are covered in Section 13.4. 13.1.1 Time Division Duplex (TDD) Three different duplex transmission methods are used in telecommunications: frequency division duplex (FDD), time division duplex (TDD) and space division duplex (SDD). The FDD method is the most common duplex method in the cellular systems. It is used, for example, in GSM, as well as with the WCDMA terminals currently com merciallly deployed in the UMTS frequency bands. The FDD method requires separate frequency bands for both WCDMA for UMTS, third edition. Edited by Harri Holma and Antti Toskala # 2004 John Wiley & Sons, Ltd ISBN: 0-470-87096-6 uplink and downlink. The TDD method uses the same frequency band but alternates the transmission direction in time. TDD is used, for example, for the digital enhanced cordless telephone (DECT). The SDD method is used in fixed-point transmission where directive antennas can be used. It is not used in cellular terminals, however, the use of beamforming techniques with FDD or TDD can be considered an SDD application as well . Figure 13.1 illustrates the operating principles of the FDD and TDD methods. The term downlink or forward link refers to transmission from the base station (fixed network side) to the mobile terminal (user equipment), and the term uplink or reverse link refers to transmission from the mobile terminal to the base station. There are some characteristics peculiar to the TDD system and these are listed below.  Utilisation of unpaired band. The TDD system can be implemented on an unpaired band while the FDD system always requires a pair of bands.  Discontinuous transmission. Switching between transmission directions requires time, and the switching transients must be controlled. To avoid corrupted transmission, the uplink and downlink transmissions require a common means of agreein g on transmission direction and allowed time to transmit. Corruption of transmission is avoided by allocating a guard period which allows uncorrupted propagation to counter the propaga- tion delay. Discontinuous transmission may also cause audible interference to audio equipment that does not comply with electromagnetic susceptibility requirements.  Interference between uplink and downlink. Since uplink and downlink share the same frequency band, the signals in these two transmission directions can interfere with each other. In FDD, this interference is completely avoided by the duplex separation of 190 MHz. In UTRA TDD, individual base stations need to be synchr onised to each other at frame level to avoid this interference. This interference is further analysed in Section 13.3.  Asymmetric uplink/downlink capacity allocation. In TDD operation, uplink and downlink are divided in the time domain. It is possible to change the duplex switching point and move capacity from uplink to downlink, or vice versa, depending on the capacity requirement between uplink and downlink.  Reciprocal channel. The fast fading depends on the frequency, and therefore, in FDD systems, the fast fading is uncorrelated between uplink and downlink. As the same Bandwidth 5 MHz Bandwidth 5 MHz Bandwidth 5 MHz FDD TDD Uplink Uplink Downlink Downlink t Guard period t Duplex separation 190 MHz ff Figure 13.1. Principles of FDD and TDD operation 412 WCDMA for UMTS [...]... duplex method in the cellular systems It is used, for example, in GSM, as well as with the WCDMA terminals currently commerciallly deployed in the UMTS frequency bands The FDD method requires separate frequency bands for both WCDMA for UMTS, third edition Edited by Harri Holma and Antti Toskala # 2004 John Wiley & Sons, Ltd ISBN: 0-470-87096-6 WCDMA for UMTS 412 uplink and downlink The TDD method uses... Prasad, R., Wideband CDMA for Third Generation Mobile Communications, Artech House, 1998, 439 [10] Holma, H., ‘A Study of UMTS Terrestrial Radio Access Performance’, Doctoral thesis, Communications Laboratory, Helsinki University of Technology, Espoo, Finland, 2003 [11] Sipila, K., Honkasalo, Z.C., Laiho-Steffens, J., Wacker, A ‘Estimation of Capacity and Required Transmission Power of WCDMA Downlink Based... ‘Physical Layer Measurements’, v.5.4 408 WCDMA for UMTS [22] Pedersen, K.I and Mogensen, P.E ‘Directional Power Based Admission Control for WCDMA Systems Using Beamforming Antenna Array Systems’, IEEE Trans on Vehicular Technology, November 2002, Vol 51, No 6, pp 1294–1303 [23] Osseiran, A and Ericson, M ‘On downlink admission control with fixed multi-beam antennas for WCDMA systems’, Proc IEEE Vehicular... Japan, May 2000, pp 100 2 100 5 [12] 3GPP Technical Specification 25 .104 ‘UTRA (BS) FDD; Radio transmission and Reception’ [13] 3GPP Technical Specification 25 .101 ‘UE Radio Transmission and Reception (FDD)’ [14] Winters, J.H., ‘Smart Antennas for Wireless Systems’, IEEE Personal Communications, Vol 5, Issue 1, February 1998, pp 23–27 [15] Paulraj, A and Chong-Ng, B ‘Space–Time Modems for Wireless Personal... UTRA FDD 13.2.3 Physical Channel Structures, Slot and Frame Format The physical frame structure is similar to that of the UTRA FDD mode The frame length is 10 ms and it has two different forms, depending on the chip rate The 3.84 Mcps TDD WCDMA for UMTS 416 Code N Code 2 Code 1 TS0 TS1 TS2 TS3 MA TS4 TS5 TS6 TS7 TS8 TS9 TS10 TS11 TS12 TS13 TS14 10 ms Figure 13.4 Frame structure of UTRA TDD The number... IEEE, Vol 85, No 7, 1997, pp 103 1 106 0 [27] Godara, L.C., ‘Application of Antenna Arrays to Mobile Communications, Part II: Beamforming and Direction-of-Arrival Considerations’, Proc IEEE, Vol 85, No 8, 1997, pp 1195– 1245 [28] Jakes, W.J (ed.), Microwave Mobile Communications, IEEE Press, New Jersey, 1974 [29] Muszynski, P., ‘Interference Rejection Rake-Combining for WCDMA , Proceedings of WPMC’98,... PIMRC’99, Osaka, Japan, September 1999, pp 52–54  410 WCDMA for UMTS [70] Divsalar, D and Simon, M K., ‘Improved CDMA performance using parallel interference cancellation’, Proc IEEE MILCOM’94, Fort Monmouth, N J USA, Oct 2–5, 1994, pp 911–917 [71] Cho, Bong Youl and Lee, Jae Hong, ‘Nonlinear parallel interference cancellation with partial cancellation for a DS-CDMA system’, IEICE Trans On Communications,... specifications for the 3rd Generation Partnership Project (3GPP), the documents TS 25.221–TS 25.224 and TS 25 .102 [1–5] are especially valuable references for obtaining information on the exact details For Release 5, the High-Speed Downlink Packet Access (HSDPA) presented for FDD in Chapter 11 has been included for TDD as well The TDD operation of HSDPA includes similar ARQ operation, use of 16 QAM modulation... Service WCDMA System’, IEEE Proc Vehicular Technology Conference, September 2001, pp 1528–1532 [19] Tiirola, E and Ylitalo, J ‘Performance Evaluation of Fixed-Beam Beamforming in WCDMA Downlink’, Proc Vehicular Technology Conference, Tokyo, Japan, May 2000, pp 700–704 [20] Pedersen, K.I., Mogensen, P.E and Ramiro-Moreno, J ‘Application and Performance of Downlink Beamforming Techniques in UMTS , IEEE... References ¨ [1] Holma, H., Soldani, D and Sipila, K ‘Simulated and Measured WCDMA Uplink Performance’, Proceedings VTC 2001 Fall, Atlantic City, NJ, USA, pp 1148–1152 [2] UMTS, Selection Procedures for the Choice of Radio Transmission Technologies of the UMTS, ETSI, v.3.1.0, 1997 ¨ [3] Laiho-Steffens, J and Lempiainen, J., ‘Impact of the Mobile Antenna Inclinations on the Polarisation Diversity Gain in DCS1800 . and Prasad, R., Wideband CDMA for Third Generation Mobile Communications, Artech House, 1998, 439. [10] Holma, H., ‘A Study of UMTS Terrestrial Radio Access Performance’, Doctoral thesis, Commu- nications. used, for example, in GSM, as well as with the WCDMA terminals currently com merciallly deployed in the UMTS frequency bands. The FDD method requires separate frequency bands for both WCDMA for UMTS, . E b =N 0 vs. number of users for a 384 kbps data service and BLER target 10 % in case 3 channel (120 km/h), the number of diversity antennas 1, 2 and 4 406 WCDMA for UMTS peak data rates exceed