Research On Symbol Synchronization In WiMAX

Wireless communications development is undergoing rapidly in recent years, with new technology emerging one after another. The wireless communications are evolving towards higher speed rate, bigger cover scope, and better mobility. Various industrial alliances and standards also correspondingly got promoted. As an alliance of the industrial broadband wireless communications, WiMAX proposed the Wireless Metropolitan Area Network technology based on the IEEE802.16 standard series. Its appearance happens to satisfy the need of wireless internet. It is also one of the solutions to the access of "the last kilometer ".IEEE802.16 standard series include altogether seven standards: 802.16, 802.16a, 802.16c, 802.16d, 802.16e, 802.16f and 802.16g. Corresponding to mobility and immobility, WiMAX supports IEEE802.16d and IEEE802.16e two standards, IEEE802.16d supports the fix broadband wireless access while IEEE802.16e supports mobile broadband wireless access. The IEEE802.16d physical layer contains five kinds of structures: SC PHY, SCa PHY, OFDM 256 PHY, OFDMA 2048 and WirelessHUMAN.This thesis mainly studied symbol synchronization technology and suitable schemes for both single-carrier (SC) PHY Layer and the multi carriers (OFDM 256) PHY Layer of the two typical physical layers in IEEE802.16d standard. Single-carrier modulation is the main modulation technology at present, but OFDM plus interleaving and channel coding also start to apply now.For single-carriers (SC) symbol synchronization, Digital filtering and squaring algorithm are mainly studied and analyzed. Theory and simulation indicate that the estimated error is non-biased and free from the effect of the carrier offset. Based on this algorithm, combined with cubic interpolator introduced by F.M.Gardner, a digital phaselock loop can be constructed. The loop is discussed and simulated in detail. Simulations indicate that the BER performance in the loop is close to that of ideal system without sampling offset for 4QAM.For multi-carrier (OFDM 256) symbol synchronization, in frame capture stage, as the Schmidl & Cox I and II algorithms have peak platform causing uncertainty of timing recovery, autocorrelation associated with coarse carrier offset estimate can be employed in allusion to long preamble. When in case of short preamble, Minn A method can get the obvious peak. In the frequency domain, based on the extraction of known inserting pilots, we infer the inverse matrix of pilots in different locations, afterward get the channel impulse response, and further find the power strongest way. At last, the delay locked loop can correct the left sampling clock deviation.The single-carrier and multi-carrier symbol synchronization schemes mentioned above include first catching (coarse synchronous) then tracking (fine synchronous) integrity steps, and the simulation platform is built up in accordance with the actual system flow structure. The simulation results prove that the two schemes can correct both sampling clock phase and largest clock frequency deviation (80ppm) stated in IEEE802.16d. Differing from previous sampling clock adjustment analog or mixed digital-analog circuits, this thesis suggests a fixed frequency clock sampling scheme, which can be implemented by all-digital circuits with simple structure, high integration.