Synchronization signals are transmitted twice per 10 ms radio frame. The PSS is located in the last OFDM symbol of the first and 11th
slot of each radio frame
which allows the UE to acquire the slot boundary timing independent of the type of cyclic prefix length. The PSS signal is the same for any given cell in every subframe in which it is transmitted (the PSS uses a sequence known as Zadoff-Chu).
The location of the SSS immediately precedes the PSS--in the before to last symbol of the first and 11th slot of each radio frame. The UE would be able to determine the CP length by checking the absolute position of the SSS. The UE would also be able to determine the position of the 10 ms frame boundary as the SSS signal alternates in a specific manner between two transmissions (the SSS uses a sequence known as M-sequences).
In the frequency domain, the PSS and SSS occupy the central six resource blocks, irrespective of the system channel bandwidth, which allows the UE to synchronize to the network without a priori knowledge of the allocated bandwidth. The synchronization sequences use 62 sub-carriers in total, with 31 sub-carriers mapped on each side of the DC sub-carrier, which is not used. This leaves 5 sub-carriers at each extremity of the 6 central RBs unused.
Next: Physical Channels
About the Author
Frank Rayal is the Chief Technology Officer and Co-Founder at Telesystem Innovations. Based in Canada, Mr. Rayal assists clients with technology and vendor evaluation, business plan and financial modeling, RFI/RFP process, RF network planning and dimensioning, and project management for field trials and network deployment, and product requirement development. Prior to founding TSI, he was Director of Product Management at Redline Communications, where he developed base stations targeted at different market segments and applications and launched end-to-end broadband wireless access networks in emerging markets. Mr. Rayal holds a BS in Electrical Engineering from Case Western Reserve University, Cleveland, OH, and a MASc and MBA from the University of Toronto. He can be reached at: firstname.lastname@example.org.
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