tailieunhanh - Wcdma for umts radio access for third genergation mobile communacations phần 10

Các tiêu chuẩn 3GPP và các chi phí thực hiện của người nhận ra các yêu cầu cơ bản cho một bộ tiếp nhận PIC. Kênh mã hóa mạnh mẽ quy định trong các yếu tố lây lan tiêu chuẩn và thường ngắn có nghĩa là SINR có thể khá thấp ở một bộ tiếp nhận, dẫn đến quyết định thăm dò không đáng tin cậy và BER cao trước khi giải mã, tăng đến 15%. | Physical Layer Performance 403 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 decisionbased 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. PIC Efficiency and Derivation of Network Level Gains We define PIC efficiency fl as the amount of own-cell interference it can remove. It is assumed that PIC cannot remove other inter-cell interference. We can write Itotal for Rake and PIC as Aotaựake Cwri T Twn T N0 1 T i KrakePj T PN total PIC 1 - 0 Iown T ilown T No 1 T i - A KpicPj T Pn where i is the ratio of other-cell interference to own-cell interference PN is the thermal noise power and we have assumed that users are homogenous each having the same received power Pj. Krake and Kpic are the number of users for Rake and PIC respectively. Kpic is selected so that Itotal rake and Itotal pic are equal . noise rises of Rake and PIC are the same. We can solve capacity gain Gcap Kpic Krake from the equations above Gcap Kpz iTT Krake 1 T i p Coverage gain is defined as the ratio of required Eb Nos for Rake and PIC when the number of users K is kept constant fl fEb No rake 1- - Gc- S No 22 8 Using the definition of Eb N0 and using Equations we get Eb No K W j W 1 1 K RPn RL - 1 T i - 3 K v Note that fl is zero for a Rake receiver. From Equations and we obtain G . fEb No rake . G Eb No p7c W 1 1 JL -ỆT i K R1 - 1 T i - fl K Lj 1 T i