Ieee 802.16d Physical Layer Technology Research

The fast growth of the Internet has witnessed diverse broad-band access techniques. The wired access represented by ADSL has taken the lead and become a major home-user broadband access mechanism. Although the wireless broadband access has not become a mainstream access technique,its unique advantages has won itself a place in the broadband market, with an ever increasing deployment.The release of IEEE 802.16d standard has been a highly influential event in the wireless broadband access business in 2004. IEEE 802.16d is devised to serve as the standard for fixed wireless broadband MAN access,incorporating many new technologies at physical and media access layer,having an advantage in system capacity and coverage range over wireless LAN systems. IEEE 802.16d employs OFDM as mandatory modulation mechanism at physical layer. Similar to other OFDM-based wireless systems, IEEE 802.16d system has difficulties in timing , frequency synchronization and channel estimation. All the three problems are discussed in this paper.First, a brief description of IEEE 802.16d is given, from brief introduction to its background, target applications, system architecture and technical features, to detailed analysis of the physical layer specification of the standard. Then, a study on timing, frequency offset estimation and channel estimation algorithm is given.On timing. We investigated the impact of timing offset on OFDM systems, and several proposed practical algorithms. According to 802.16d systems' characteristics a new timing algorithm is proposed after analyzing Schmidl algorithm and the joint auto-cross correlation estimation algorithm. This new algorithm has very high sensitivity, and works well under SNR lower than -15dB, with predictable stable peak values.On frequency synchronizaiton.For fractional frequency offset estimation, the adoption of joint estimation with two preamble symbols significantly reduced the effect of noise.For integer frequency offset estimation, we analyze a sequence auto-correlation based algorithm, and extend the algorithm into frequency selective channel case. For frequency offset tracking, the constellation rotation is effectively reduced by using the eight pilots in the symbol to track the phase offset.Simulation results show this algorithm has similar performance with no-frequency-offset systems.On channel estimation .Simulated frequency-domain LS, MMSE, time-domain LS and the new time-domain auto-correlation based algorithm. Simulation results show the four algorithms do not have significant performance difference, because of the abundance of pilots in preamble. The new time-domain auto-correlation based algorithm has similar performance with MMSE, while less sensitive to the channel characteristics and has lower complexity.