Pilot Design for Inter-cell Interference Mitigation and Handover Decision Scheme Based on Zadoff-Chu Sequence in OFDM Systems
Date Issued
2011
Date
2011
Author(s)
Chen, Yen-Tsang
Abstract
Orthogonal frequency division multiplexing (OFDM) has been widely considered to be adopted in the future wideband wireless communication systems including the Long-Term Evolution (LTE) because it has high spectral efficiency and can avoid intra-cell interference. The cellular mobile communication network based on orthogonal frequency division multiplexing access (OFDMA) also can achieve frequency reuse of one, which means that all cells in the system can use the same frequency band to serve each own users. In OFDM systems the orthogonality among subcarriers is critically demanded. Although some factors like carrier frequency and phase shift will result in inter-carrier interference, it can be depressed through advanced wireless signal processing algorithm in the physical layer. Therefore, it is thought that intra-cell interference is very small in OFDM systems. The major interference which affects the system performance is the inter-cell interference (ICI).
Channel estimation is an important issue in OFDM systems. Pilot sequences are often multiplexed into the data to estimate the wireless channel gain. Both pilot sequences and their placement can affect the mean square error (MSE) of the least squares (LS) channel estimation. In order to make neighboring cells use the same frequency band to serve its own users and in the meanwhile mitigate the inter-cell interference, we choose Zadoff-Chu sequences as pilot design since its cross-correlation has good orthogonal property. Therefore, assigning neighboring cells different and orthogonal Zadoff-Chu sequences can mitigate the ICI efficiently and improve the downlink and uplink transmission performance between the base station and the users.
Besides, we consider that the user located at the crossover area of multiple base station coverage can be seriously interfered with the interferers in other cells in the uplink; as a result, the serving base station can not demodulate the user’s signal correctly and excessive uplink transmission errors will result poor Quality of Service (QoS). To solve this problem, we propose a handover decision scheme, where we use the cross-correlation property of Zadoff-Chu sequences to estimate interference power seen by each neighboring base station. Then the serving base station will provide interference information of each neighboring base station to the user. The user can select the target base station which has least interference as the serving base station.
Subjects
inter-cell interference (ICI)
Zadoff-Chu sequence
pilot
channel estimate
handover
Type
thesis
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