ex base) indicates the code cv chosen from the sequence matrix C (i.e., the row of the Hadamard matrix of maximum length N = 16). The decimal numbers indicate the sequence length over the time domain. Note that the suggested scheme covers different sequence length n = {1,2,4,8,16} because the sequence pattern repeats itself every n rows. Thus, the system may benefit from more precise channel estimation for increasing sequence length N. The suggested scheme assigning virtual pilot sequences to the multicell system is translational invariant with respect to the estimation error. Its block orthogonality is sustained even after a cyclic shift. Note that the suggested scheme can be easily extended © 2009 by Taylor & Francis Group, LLC Cooperative Transmission Schemes 0.001 SC Power/mean Symbol Power p(dB) Figure 7.17 Normalized duration of fades. 111111111 1-1 1-1 1-1 1-1 1-1 1-1 1-1 1-1 1 1-1-1 1 1-1-1 1 1-1-1 11-1-1 1-1-11 1-1-1 1-1-111-1-1 1 11-1-1-1-1-1 1111-1-1-1-1 1-1-1 1-1 1 1-1 1-1-11-1 1 1 1-1-1-1-11 1 1-1-1-1-11 1 1-1-1 1-111-1 1-1-11-111-1 1111111 -1-1-1-1-1-1-1-1 1-1 1-1-11-11-11-11 11-1-1-1-111-1-11 1-1-1 1-1 11-1-111-1 1 1-1-1-1-1-1-1-1-11111 1-11-1-11-1 1-11-111-11- 1-1-1-111-1-11111-1-1 1-1-1 1-111-1-111-1 1-1-1 1 Figure 7.18 Left: pilot reuse pattern based on orthogonal code sequence (e.g., Hadamard) in a triple-sectorized cellular system. Right: Hadamard sequences spread over space (rows) and time (columns) domains. Hex-base numbers indi- cate sites with the same virtual pilot sequence [37]. C 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology top-1 signal top-2 signal top-3 signal top-4 signal top-5 signal top-1 signal top-2 signal top-3 signal top-4 signal top-5 signal TTI (1 ms) TTI (1 ms) (a) Pseudo-random (b) Hadamard, Fixed Pattern Figure 7.19 Normalized MSE obtained for the correlation estimator, in case of a static channel, for the five strongest sectors. to the case of larger correlation length. Resulting performance improvements of channel estima